Progression in primary school children's conceptions of burning: Toward an understanding of the...

Research in Science Education, 1999, 29(3), 295-312

Progression in Primary School Children's Conceptions of Burning: Toward an Understanding of the Concept of Substance

Sri Rahayu IKIP Malang

Russell Tytler Dealdn University

Abstract

Children's conceptions of burning were explored through observation and discussion or a number of challenging phenomena. Analysis of written responses showed that children's conceptions are both specific and contextually based, and that there is little coherence in the use of any one conception across phenomena. Progression across the primary school years can be described, however, in terms of children's growing confidence with the idea of transformation of substances and the analysis relates this to a model based on changing commitments to the notion of substance defined by properties, rather than history. The conceptual trajectories described in the study are broadly consistent with previous studies of secondary school children.

Chemical Change and Burning

From the beginning of the remarkable flowering of research into student conceptions in science there has been an interest in studying the conceptions of students of different ages, in order to give insight into the way these ideas develop (e.g., Osborne & Cosgrove, 1983; Carey, 1985). Such studies of conceptual progression are useful in identifying critical developmental ideas and also in informing curriculum sequencing in particular content areas (Driver, Leach, Scott, & Wood- Robinson, 1994). One of the major content areas such research has focused on has been changes to matter, including chemical change, and this study aims to contribute to our understandings in this area.

Some of the more dramatic natural phenomena children experience in their daily lives involve chemical reactions in which the nature of substances changes irreversibly. The process of burning is probably the most common of such experiences (Driver, 1985, p. 145). From early childhood, children will inevitably have observed a variety of instances of burning: a candle burns, a sheet of paper catches fire, food is barbequed, skin reddens when exposed to the sun. They will have been exposed to the language with which such things are commonly described. They come to school with a history of experience and a personal perspective on burning.

Burning is not a straightforward phenomenon. Ross (1991) describes two opposing processes represented by the word "bum." The first, "char-burning," involves an endothermic decomposition such as occurs when things char, or our skin is damaged by heat, or food is digested. The second, "flarn~e burning," involves the exothermic reaction of fuels with oxygen, including the respiration process. In "char-burning," the heat causes evaporation or giving offvapour or smoke. The mixture of vapour or smoke with oxygen can ignite, initiating a "flame-burning" process which releases heat back to the environment. The current study includes both types, but mainly focuses on students' understandings of what happens when flame burning occurs.

296 ILAHAY'U AND TYTLER

The Nature of Students" Ideas about Burning

Students' understandings about burning have been investigated by researchers in a variety of countries, mainly at the secondary schooling level. These studies are generally framed within the context of understandings about changes to materials and chemical change in particular. Schollum and Happs (1982), in a study of Australasian students ranging in age from 10 years to 18 years, identified a range of children's and adolescents' views concerning burning which differed from scientists' views, including: air is not actively involved in burning; a substance is not used up, nor new substances formed in the burning process; heat is thought of as a substance is formed in the burning process; particles can be destroyed in a flame. Meheut, Saltiel and Tiberghien (1985) found that 11-12 year old pupils had not one but a range of different views of burning, influenced by perceptual features of the process. Some combustibles were believed to be unable to bum but only to melt or evaporate. For instance, combustion of a candle is interpreted as the wax melting, iron is said to melt, but not to bum, and the combustion of alcohol in an alcohol lamp is explained as alcohol turning into vapour. Materials such as wood, cardboard, or a candle wick change into something else, with quite different properties (e.g. color or smell) and are often called by a different name (cinders, carbon). Where pupils recognizsed that air has a role, they thought of it undergoing transformation independent of the combustible material.

Children's and adolescents' views are thus a long way from an understanding of the burning process as an interaction of chemicals. Meheut et al. (1985, p. 90) argue that,

"in the pupils" mind, the modification of the properties of an object in the course of a combustion does not result fi'om the interaction between several substances but fi'om separate transformations of each of the substances composing the object ... Transformations are thought of as involving the substances separately, rather than representing interactions between several substances.

It seems that students think in terms of an ongoing history for each of the substances involved in the burning process.

BouJaoude (1991) also emphasizsed the contextual nature of students' ideas about burning. Using an interview-about-instances technique to investigate junior high school students' understandings about the concept of burning, he found that students: (a) based their understandings on the concrete and observable changes that took place during burning; Co) used memorised information to explain their observations; and (c) held fragmented, inconsistent, and task-specific understandings. There seemed to be no coherent set of ideas about burning that the students were using across the events they observed. Different phenomena were quite differently viewed: wax melts, alcohol evaporates, and bread changes color. BouJaoude describes his subjects' understandings as context bound, task specific, and "speeializsed in the particular and the concrete (p. 698). They used them to create explanations for specific activities and not to produce 'kmiversal truth" (p. 699).

Progression in Students' Understandings of Burning

Andersson (1986, 1990) proposed a classification system which attempted to make sense of students' ideas about physical and chemical change, including combustion, reported in the literature. His scheme involves five categories:

1 . It is just like that: No explanation is given for the disappearance of substances. 2. Displacement: A substance appears at a given place because it has been displaced from

elsewhere. 3. Modification: What appears to be a new substance is in actual fact the same substance as

before.

TOWARD AN UNDERSTANDING OF THE CONCEPT OF SUBSTANCE 297

4. Transmutation: A given substance is transformed into a new one. 5. Chemical interaction: The original substance can interact with another one to form a new

substance.

While these are not intended to be strictly sequential, some studies have interpreted them as a "hierarchy of increasing cognitive demand" (Krnel, Watson, & Glazar, 1998, p. 276). The conceptions identified by Sehollum and Happs (1982) and Meheut, Saltiel and Tiberghien (1985), for upper primary and secondary school students, can be seen to be mainly representative of the modification and transmutation categories.

Prieto, Watson and Dillon (1992) used a modification of Andersson's scheme to make sense of pupil's (age 14-15) ideas about the process of burning. They analysed students' views on the role of oxygen and of the flame, and on the relationship of products and reactants, using the modification/transmutation/chemical reaction categories. They described progression of student understanding of burning using a model involving two dimensions--growing recognition of the interactions involved in a chemical reaction, and the separation of burning phenomena from physical change processes. They identified a number of students who appeared to be in a transition stage between a transmutation view and a chemical reaction view of burning. They argued that students' views are not fundamentally fragmented, as BouJaoude (1991) claimed, but that inconsistency of explanations is better viewed "in terms of a pupil struggling to develop a new explanatory model to replace one which is no longer adequate to explain the range of phenomena" (p. 338). The view that students' ideas are fragmented and inconsistent on the one hand, and that they can be characterizsed as representing stages in a general progression of understanding, on the other, are not incompatible. There have been a number of studies that explore the context bound and inconsistent nature of student conceptions (diSessa, 1988, 1993; Claxton, 1993; Svensson, 1989; Tytler, 1998a).

Interviews of some of the same students 16 months later (Watson & Dillon, 1996) showed no progression in students' ability to separate chemical from physical change processes, but they did fred an increase in the number of students using chemical change explanations. It is not clear, however, how significant this change is, given that it seems to be mainly related to students being able to name more reactants and products correctly.

Johnson (1997b) argues that combustion is a particularly difficult example of chemical change since it involves the gaseous state in both reactants and products, and decomposition as well as synthesis. Johnson used a set of staged categories to describe his students" progression of views on a burning candle, that are different to Andersson's categories but can be related to them. At a lower level, students think that the missing wax either simply evaporates or earmot be accounted for (a displacement/modification idea). At the next level they believe the wax becomes the water and/or carbon dioxide but do not recognizse the role of oxygen. This could be interpreted as one version of a transmutation idea. The next level involves a rudimentary awareness of chemical change, in that the interaction with oxygen is recognizsed, and it is understood that the water and carbon dioxide are not pre-formed in the wax.

There have been few studies which attempt to trace the progression of primary school children's ideas about burning. A large scale survey study conducted with Victorian primary school children (Adams, Doig, & Rosier, 1991), which included a limited number of probes concerning chemical change and burning, identified no clear sequence concerning the progression of children's ideas of chemical change, beyond a growing recognition of non-observable changes to materials.

298 RAHAYU AND TYTLER

The Concept of Substance

Dickinson (1987) studied the development of children's conception of"material kind" over the age span from 4 to 12 years. He found that children moved from a tendency to classify things as objects, to a confident understanding of material that was independent of object, over these years. Between ages four to nine, for instance, children became much more confident in recognizsing that when an object is ground into a powder, the material remains the same. Smith, Carey and Wiser (1985) reported broadly similar findings. Kmel, et al. (1998) argue that this difficulty relates to children's inability to distinguish between extensive and intensive properties. The task, for children from four years, is to develop a concept of material that is independent from object. One can imagine that, having mastered this by about the age of I0, students younger than this would then have considerable trouble dealing with changes to materials that involve their decomposition or reconstitution into new substances that bear little relation, in terms of properties, to the originals. The major intellectual task for them, as it was in the history of science, is to understand what remains constant in the face of such obvious change.

The concept of substance is central in chemistry (Stavridou & Solomonidou, 1989; Johnson, 1996). For the chemist, materials can be made of pure substances, or mixtures of these, and substances can be either elements or compounds. Johnson (1997a) argues that a consideration of the way properties (such as melting point) are used to identify substances should be a central focus of chemistry teaching. In a longitudinal study of students over a period of three years (ages 11-14), mainly using interviews, he identified difficulties students experienced with both physical and chemical change concepts, and their responses to teaching sequences dealing with these concepts. Initially, students tended to view the integrity of a substance in terms of its history, rather than its properties. The question of a reaction product, "Is this the same substance?" was answered in terms of where it had come from. For instance, rust is still fundamentally iron, since it came from iron. Johnson notes that examples of this type of thinking have previously been discussed by Pfundt (1981), and de Vos and Verdonk (1987). Johnson asserts that, in discussing the relationship between iron and rust,

pupils simply did not have the possibility of substances changing into other substances as a part of their thinking. They did not entertain the idea of a chemical change. In trying to account for the observations, the pupils could only draw on the historical ideas of "origin" and "mixing," or answer a different question.

This "historical" view of substances underlies Andersson's categories of displacement and modification, since with these conceptions each of the materials retains its essential individual identity, even though the properties may change. Such a view obscures, of course, the fundamental distinction between physical and chemical change (Driver et al., 1994). The idea of substances reconfiguring into other substances with fundamentally different identities cannot make sense until one has a model of how substances can be compounded forms of simpler substances, with properties quite distinct from those of their constituents. Fensham (1994) argues the case for a non particle introduction to chemistry, but Johnson (1997a) contends that a particle theory is a necessary precursor to any adequate understanding of chemical change. Skamp (1998), using a comparative study of lesson sequences in Years 5 and 7, found positive effects from teaching about atoms and molecules in the primary school.


Purpose

This study investigated ideas about burning held by primary school children of ages 6, 8 and 11. Most of the previous studies have involved students in secondary school, and all have been over the age of 10 years. We aimed to map out the conceptual trajectory followed by primary school students in relation to their ideas about changes to materials, and explore whether the ideas of these younger students form a coherent sequence leading into older students' ideas as described in previous studies.

Driver et al. (1994, p. 85) argue that cross-age studies,

can be interpreted from an evolutionary perspective on knowledge acquisition. From this perspective, learning within a particular domain can be characterised in terms of progress through a sequence of concepmalizsations which portray significant steps in the way knowledge within the given domain is represented. This sequence of conceptualizsations we call a conceptual trajectory.

We were interested to explore the critical conceptual advances that mark progression in students' growing understanding of substance. We also investigated the consistency with which children apply particular conceptions across different contexts, an issue which bears directly on the nature of science knowledge, and of conceptual change (Tytler, 1998a, b).

Research Design and Methods

We used a similar but simplified methodology to that previously used to study children's conceptions of air pressure (Tytler, 1998a). The children were in Years 1, 3 and 6 in an Australian primary school. There were 21, 26 and 26 children in the respective years. They had not covered any "changes to materials" work in the recent past, and it is unlikely they had been exposed to explicit teaching about burning, or to chemical change. The older children could be expected to have covered topics of dissolving and melting in their school science. The children were taken through a range of activities on burning, working in groups of seven to nine under the supervision of an adult. For each activity, the adult played the role of facilitator, seeking clarification and challenging as necessary. For some of the activities a predict-observe-explain technique (White & Gunstone, 1992) was used. The activities represented a range of burning contexts, and the questions probed children's conceptions of the nature of the changes to materials, during combustion. The activities were:

(a) A burning candle is discussed. A jar is put over it and the flame is extinguished. Carbon forms on the jar.

(b) Steel wool is burnt. (c) Paper is burnt, and its weight compared with an unburnt piece. (d) Chocolate, butter, candle wax, ice, are heated in a frypan, and allowed to cool. (e) A kerosene lamp is observed. The flame increases and smokes when the handle is turned. .(f) A methylated spirits camping stove bums, and a large beaker is put over it. Water forms on

the inside of the jar and the stove is extinguished. (g) Burnt toast is examined and compared to bread.

Children predicted, with reasons, what they thought would happen in each case, before the activity was demonstrated. They discussed the result as a group, to suggest possible explanations, but the group leader avoided imposing a conclusion. The discussion was recorded. Each child then wrote a response to questions associated with each activity. The questions focussed on what


happens to the substance in the burning process, what the products are and how they are formed, and in some eases what is the role of air in the burning process. By allowing discussion with peers before seeking children's written responses, we maximizse the chance of getting their considered beliefs about the phenomena, since they have a range of opinions to respond to, and are not forced to commit themselves to an ill considered off-the-cuff response. Two children from each year level, nominated by the teacher to represent divergent abilities, were then interviewed concerning these same phenomena to gain some further insight into their responses.

Results and Discussion

The written responses to questions about the nature and products of burning were coded using a category system that was initially based on the work of Andersson (1986, 1990), but was emergent to some extent since it was modified to take better account of the responses. Validation of the coding was achieved by two means. Firstly, both authors coded a subset of responses independently, leading to an 80% agreement rate. The responses where the coding differed were discussed in detail and recoded. Secondly, a code/recode technique was used, with a two week gap, for all the responses, resulting in 95% correspondence and leading to a further and final recoding.

There was one major deviation from Andersson's categories, arising out of this process. Our "transformation'" category (see Figure 1) is equivalent to Andersson's (1986, 1990) "Wansmutation of substances" category, but we have separated it from the substance----energy transmutation category and renamed it. We conclude that this conception represents an important advance toward the scientific conception of chemical interaction, involving the recognition that new substances are appearing that are different to the originals. It is unfortunate that Andersson consistently uses the idea that steel wool when burnt turns to carbon as his main example of the transmutation of substances, giving some historical credence to his terminology through an echo with the alchemists' quest to transmute lead into gold. By linking it in his categorizsation system with the idea that substances can transmute into heat or energy, he further reinforces the interpretation of this idea as a misconception. We would argue that Andersson's analysis misses the important point that the transformation idea represents an insight that is fundamentally generative in laying the groundwork for an understanding of chemical interaction.

Figure 1 shows the categories established for analysing children's conceptions of chemical change, arising out of this process.

Progression of Student Conceptions

Table 1 shows the change in children's use of these conceptual categories across the primary school years. Most of these categories do not show any change with age at all, calling into question the claim of Kmel et al. (1998) that they represent a hierarchy of increasing cognitive demand, at least in respect to combustion. The categories which make up the bulk of views; simple description, associative modes of thinking, and modification, seem to be equally accessible to all age groups in interpreting combustion. The conception that substances are created or destroyed in a flame, or in association with heat, was also equally accessible to children of all ages. This was one category within the transmutation conception described by Andersson (1986), but it seems, from these results, to be somewhat of a dead end in terms of progression of understanding. There is some indication of progression in use of the displacement idea from Year 1 to 6, but the real change Occurs with the older children increasingly using a transformation conception. We also see the beginnings of the appearance of a chemical reaction conception at Year 6, but with very few instances. This conception seemed entirely inaccessible to the younger children.


Category Description and examples Simple description "It's just like that." e.g., The flame goes bigger.

Associations These refer to a range of styles of associative thinking, including: �9 Everyday assoeiatious / inferences e.g. The higher the wick the higher the

flame. The wax burnt. �9 Imported analogies e.g. The fire doesn't have enough air to breathe. �9 Potency of substances to cause effects, e.g. A fire needs air to keep going.

Displacement Substances are not changed, but reappear in different places. The change is explained in terms of the same material moving from place to place. Sometimes the origin of the substance is obscure. e.g. The steam got trapped in the steel wool but there were holes and the steam goes out leaving the black material.

Modification A substance retains its identity but changes state (possibly reversibly), or properties due to the burning. e.g. The wax melts and turns into a liquid. The toast is actually turning black and the outside part of it goes all crusty.

Transmutation Involving a mixing of categories of heat, flame, energy and substance. This mainly occurred with references to the flame being the source of products. e.g. It is soot, it comes from the flame (steel wool).

Transformation of substance

A substance is transformed into a new substance or part of a substance is changed. In these explanations-there is a clear reference to new substances being produced or the reactants being used up. e.g. It bums then it goes black into charcoal. It took the oxygen flow and stopped the flame from burning up oxygen.

Chemical reaction Interaction of two substances forms a new substance. This category is seldom used by these primary school children, and tends to be rudimentary and confused. e.g. The candle bums the oxygen. It is being changed into carbon which makes the wick go black. Soot is carbon dioxide that the candle does not need anymore. The soot comes from the candle burning air.

Figure 1. Coding categories for the written responses.

The finding o f previous researchers that students' views o f burning are very context bound, and different for different types o f substance, is born out by our findings. Even if one looks at questions that are similar, for different substances that are burnt, students' responses show that they use quite different ideas to explain what happens for the different burning phenomena. As an exampl e, the Year 6 responses to the question, "What happens to the ... when it is burnt?" the percentage breakdown into the coding categories is given in Table 2.


Table 1 Percentage of Responses in Each Coding Category, for Students in Years 1, 3 and 6.

Year 1 Year 3 Year 6 ..Category of response (n=272) (n=350) (n---362) Simple description 15.8 12.3 10.8 Everyday associations / inferences 7.0 5.7 8.0 Imported analogies 2.6 4.0 1.9 Potency of substance 9.6 11.7 13.0 Displacement 5.1 6.3 10.6 Modification 21.7 18.8 22.7 Transmutation 7.4 9.4 5.8 Transformation 4.4 8.0 19.9 Chemical reaction 0.0 0.0 0.8 Uncodeable 26.5 23.7 6.4

Note: Each written response was assigned to only one category. The responses were mainly short, containing only one idea.

Table 2 Percentage Breakdown of Year 6 Responses to the Question "What happens to the ... when it is burnt?" (n =26)

Category/substance Candle Steel Paper Toast Simple description 46.2 3.8 3.8 7.7 Associations 19.2 3.8 7.7 23.1 Modification 19.2 88.5 53.8 34.6 Transformation 15.4 3.8 30.8 26.9 Uncodable 0 0 3.8 7.7

The high proportion of "simple descriptions" for the candle we interpret as being due to the fact that students are very familiar with the candle, and took the question to refer to the object, rather than the wick or the wax which is the fuel. For students of this age, often the wax is not thought to be involved in the burning process (BouJaoude, 1991; Johnson, 1997b). The fact that students tended to talk of the steel wool as being modified, rather than transformed, is perhaps because they feel that steel has more integrity as a substance than paper or toast, and also because they did not have a separate name for the residue (carbon, or soot). Meheut et al. (1985) found that students did not expect iron to be able to bum at all.

The Year 6 responses to the question relating to the products of combustion (e.g. What is the ..... ? Where does it come from?), shown in Table 3, yielded quite a different pattern of ideas. The concentration of responses in the modification and transformation categories for questions relating to the material being burnt, is replaced by a concentration on displacement, transmutation ("It comes from the flame"), and transformation.


Table 3 Percentage Breakdown of Year 6 Responses to the Question "What is t he . . . ? Where does it come from?'" (n=26)

Category/substance Soot on glass Steel wool Water on glass from candle residue from meths

Displacement 30.7 26.9 65.4 Modification 0 11.5 15.4 Transmutation 26.9 30.7 I 1.5 Transformation 23.1 19.2 0 Chemical reaction 11.5 0 0 Uncodable 7.7 I 1.5 7.7

These categories do not seem to represent coherent ways of looking at a range of burning phenomena, as might be implied by the term "alternative frameworks" (Driver & Easley, 1978), but are ideas that students apply specifically and contextually. They use different conceptions not only for different burning phenomena, but also for discussing products compared to reactants. Even for students who had access to the transformation conception, which one might expect to allow a coherent view of how the combustible material changes into the burning products, there was little consistency. An analysis of the data represented in Table I showed that, of the 31 students at any level who used this conception, 19 used it only once out of more than I0 responses, and only 5 students used it both in a question relating to products, and also regarding changes to an original material.

However, despite this inconsistency of use, it seems clear that the important change in views of chemical change over the primary school years relates to students increasing access to this idea. It has in common with the chemical reaction conception the view that material is transformed into different substances having a different identity.

Most of the work in student conceptions of burning has taken place at middle secondary school level, where Prieto et al. (1992) claim that students are in the process of making the transition from a transformation to a chemical reactions view. This study has allowed a look at what is happening with younger children, and it is interesting to match these results with those of older children, from the literature. Figure 2 plots the percentage of students in this, and other studies, expressing transformation views. The comparison is somewhat artificial, given the consistent findings in both this and other studies that context is critical in determining student views, and also the different interpretations that may have been put on the idea of transmutation/transformation. The results show, however, a broadly consistent increase in the transformation idea compatible with our findings.

Prieto et al.'s (1992) and Watson and Dillon's (1998) results relate to students' written responses across a range of phenomena. The percentage is interpreted from their breakdown of the number of explanations that comprised their transmutation, transitional and chemical reaction categorizsations. These students would have been exposed, of course, to quite a deal of explicit teaching about chemical change in the secondary school BouJaoude's result related to the 7 of his 20 students who believed that oxygen is transformed into carbon dioxide, so is representative of only the one phenomenon, as are Johnson's (1997b) results which relate to the number of students who, during interview, thought the wax in the candle becomes water and/or carbon dioxide, as distinct from evaporating or disappearing. Our results show a reasonable consistency with the interpreted results of Boujaoude, and Prieto et al. The somewhat lower result for Johnson's interviewees most likely relates to the difficulty of the question concerning the role of wax in a candle, compared to the specific cues provided by our activities.


P e r c e n t a g e e x p r e s s i n g the u'ansfonnation concepcion 100

5O

Current study I I 5

Pricto et al. @

~ n and Dillon

B o ~ a o y @

Current study .i ~" ,0

~ ~ ~/~dle., Johnson

I I I I ! I I I I I F- I0 15 Age

Figure 2. The percentage of explanations involving the transformation conception, against age.

For the chemical reaction conception, the literature shows a clear effect due to context, with the conception more difficult, for instance, in the case of car exhausts than for rusting copper (Andersson, 1986). The different studies indicate increased use of the idea between the ages of 12 and 15, with 10% or less of 12/13 year olds (Johnson, 1997b; Andersson, 1986) and possibly up to 30% of 15 year olds (Watson & Dillon, 1996) using the idea in some contexts. These findings are broadly consistent with the extremely marginal use of the idea by Year 6 students in our study.

In terms of progression of ideas about chemical change across the primary school years, then, the picture is complex. There are many associative and perceptual ideas that children of all ages have access to and use to a greater or lesser extent depending on the question or context, a finding that echoes the claims of BouJouade (1991). The conceptions of modification and displacement are also used by all age groups. Underneath this complex, context bound picture, though, we can discern a growing confidence with the conception that substances can be transformed.

Progression and the Transformation Conception

.The idea of transformation involves an understanding that in a burning reaction, substances change into other substances that should be considered to have a different identity. It represents a break from the view that the products of any change should be interpreted in terms of the "historical" integrity of substances through any change process. For some of the written responses this was evidenced by students calling the products of burning by a different name, such as soot, or ashes. From such short written response it is hard to know what view exactly a student has of the relationship between combustible material and the residue. It could be, as Johnson (1997a) points out, that students might think that ash, even though it has a different name, is really the same


thing as the paper, but modified. It could be argued, however, that the fact that there are different names for combustion products represents a cultural recognition that they are distinct in important ways, and that an increased tendency to use a separate name indicates a greater recognition of the possibility that new substances are being formed. Ash is not the same stuff as wood. In what respect they are different, for these children, would need f-uther probing, but the difference in name in itself acts as a marker for recognizsing a transformation of some kind. In a parallel study of chemical reactions, we have found that between Years 4 and 6, children increasingly recognizse oxygen and carbon dioxide as entities, and correspondingly they seem able to respond more productively than younger children to teaching sequences involving these gases.

The children's written responses show clearly the contextual and complex ways they use ideas to generate interpretations of the burning process. In terms of progression, the significant changes relate to a decrease in the "uncodable" category and an increase in the recognition that substances are transformed in the burning process. The interpretation of what such a transformation means is made difficult by the brevity of the written responses, and the way in which language can act to obscure meaning. The interviews allowed us more insight into the clarity with which children of different ages held and expressed specific conceptions of burning.

Specific Conceptions of Burning: The Interview Transcripts

The products of burning

For some of the activities the combustion product seems to appear out o f the flame (smoke, or soot from a candle forming on ajar). For others, the product was more obviously related to the initial substance as a residue by virtue of location (e.g. the ash from burnt paper, the oxide from the steel wool). In this latter case, the two younger children especially were inclined to a "modification" conception, maintaining a commitment to the historical integrity of the substance.

Int: Hanna (Yr 1):

Do you think that's steel wool or changed into something else? Still ..... steel wool..., because it is sort of like the steam burned it out... (and the paper is) ... still paper but it's black and it's squashed up and crunched.

It seems possible that the perceptual cues embedded in these phenomena led children to focus on the object rather than the material (see Krnel et al., 1998, p. 283), triggering a modification interpretation. This conception is in fact less sophisticated than the displacement idea applied to the other phenomena, which involved the notion of the material being composed of a range of substances.

In order to probe what the children might mean by material being "the same," or "different," we asked each of them whether, if the products of the various experiments were taken to scientists in a laboratory, they would be able to tell where they came from. Mark (Yr 1) felt the soot residues from the kerosene and candle would be distinguishable, because they arose from different substances. Both children believed these substances maintained their essential integrity through the burning process.

Alan, from Year 3, thought the remains of the paper was "still paper just black and gets delicate," and the residue from the steel wool "is still the same, but just more black.'" For soot from the kerosene that deposited at the top of the lamp he seemed clear it was a new substance:

Int:

Alan:

Suppose what we're asking is it we took took a little bit of that soot and gave it to scientists to analyse it. Do they say this is kerosene or ... just soot? I think it'd be just soot.


Lola, from Year 3, was not certain whether the burnt steel wool residue, ground up, would be identifiable. It is often hard to tell if children are taking a modification or transformation view. Indeed, perhaps for them the distinction is meaningless, only making sense from the perspective of an understanding of substance that ties it clearly to properties, and ultimately to its chemical composition. These children do not have access to either of these ideas. Jay, from Year 6, had a range of ideas about the relationship of the combustible material to the residue:

Jay (Yr 6): Yes...it's still paper but soot inside of it ... like soaking into paper and then taking over.

And for toast:

Jay: Int: Jay:

It's like a bum mark, it's charcoal caused by burning, by the toaster. So, do you think it came from the bread or outside the bread? No, the fire. The flame.

None of the children interviewed seemed to countenance that the black stuff from paper or toast may be the same substance (carbon) transformed out of different materials. They do not have the requisite knowledge to make sense of how such a thing could happen. It seems, reasonable, therefore, that they would expect that scientists could do tests to uncover the history of the substance, even if they would be willing to say it should not be called the same name as the unburnt material. Thus, even when the interviewees seemed to be expressing a Wansformation idea, when pushed they retained a belief in some sense o f the historical integrity of the substance.

There were component understandings that affected children's ability to interpret the evidence presented by the activities. For instance, Alan (Yr 3) was able to interpret the loss of weight of the burning paper to a redistribution of substance in a decomposition transformation:

Alan: Int: Alan:

� 9 it's just paper but it's black and then lighter. Right. Why was it lighter? Where did the extra weight go? I think it (the extra weight) gets up to the air . . , really broke down. So you couldn't see it.

Neither o f the younger (Yr 1) children, however, had access to the concepts that would allow them to make sense of the evidence presented by this weight change. They thought the weight was related to position.

I n t :

Markfgr 1): Hanna (Yr 1):

Why was the paper lighter when it was burnt? Because it was sort of scrunched up and most of the paper was off the weight�9 Cos, the piece of paper ... that was higher than the other.

When asked about products of burning that were not clearly a residue of the material being burnt, most children identified the flame or heat as the source, but were unclear about the relationship o f the flame to the substances.

Flanna (Yr 1): It (the black deposit on the kerosene lamp) is black steam. (It comes from) the fire.

Lola (Yr 6): The fire makes it, it's sort of air but darker.

The fog produced on the inside of the jar placed over the methytated spirits burner caused problems. Children often took a displacement perspective on its origin, arguing that there must have been water in the fuel. This is consistent with previous researchers' findings (e.g., BouJaoude,


1991). A few children in Year 3 and Year 6 knew the term carbon dioxide as the product of burning, associating this with human respiration.

Lola CYr 6): ... well, if you breathe in oxygen, you breathe out carbon dioxide.

The role of oxygen in the process of burning

In the case of the questions related to putting a ja r over the top of the candle or the camping stove, most of children in their written explanations made a strong link between burning and the presence of air or oxygen. 64% of children in Year 1, 90% in Year 3, and 96% in Year 6 explained the flame being extinguished in terms of the amount of oxygen/air inside the jar.

Some of the children used anthropomorphic images in their responses to describe the role of air in the burning process. For instance, the candle "breathed" the air. Such associations are supported by common language. Beyond its being needed, the role of oxygen was not clear, especially in the responses of the younger children, a finding that echoes earlier studies (e.g., Driver, 1985). Few even of the older children implied that oxygen was transformed or interacted with other substances in the process of burning. The interviews conf'n'med that the younger children were quite confused about the role of air or oxygen.

H (Yr I): A (Yr 3):

It goes away. Hm...it got trapped out the glass jar...it just comes out when you put it (jar) down...I think it's coming out.

The older children had a much surer knowledge, expressing a transformation idea that seemed associated with their knowledge of carbon dioxide as a product.

Int- L CYr 6):

J CYr 6):

I f I put a glass jar over the top of the candle, what happens? It would go out...Because it kind of sucks up the oxygen and it needs oxygen to stay alight and so it goes out...that's no more oxygen. I mean sort of the oxygen changes into carbon dioxide. Well, it would go out because the oxygen would eventually run out inside the jar ... because the flame would bum it up and turn into carbon dioxide.

Discussion: Progression of Ideas About Burning

Analysis o f the interviews and transcripts of discussions presented a picture consistent with the findings from the written responses. It is clear from the interviews, however, that the complexity of language use otten makes it difficult to ascribe a definite meaning to children's explanations in terms of adult conceptions such as modification or transformation. The group discussions highlighted other aspects of progression in children's ability to make sense of these phenomena, associated with experience and with language. As children move through the primary school years, they gain:

(a) access to a richer range of associations and contexts with which to connect ideas, such as associations of heat with moisture, and examples of this;

(b) access to a range of subsidiary concepts that are important in understanding burning, such as a concept of fuel, of gas, of weight, and a sharper sense of differences between changes of state (e.g., melting) and burning. These are matched by an increased vocabulary (e.g., oxygen, carbon dioxide) and an increasingly sharp distinction between categories (e.g., the distinction between steam and smoke, or dissolving and melting);


(r control over more complex causal explanations, and the levels of reasoning this opens up. Thus they are able to construct explanations of multi-stage events. The older children seemed able to support their explanations with more carefully thought out justifications and consistency cheeks.

Over the primary school years, children undergo a gradual but significant change of view concerning the way in which they conceptualizse substances and changes to substances. Throughout the primary school years there is considerable change in conceptions of states of matter, and physical change (e.g., Tyfler, 1997). In the last years of primary school we begin to see the establishment of the conception of transformation of substances through blaming. Despite this, many of their earlier ideas and associations form and ongoing aspect of their view of burning phenomena. For instance, the idea that products must have been present in the original substance in some form, that the residue is a modified form of the original substance, or the idea that a flame can be the source of materials.

The shift to a transformation view requires an reappraisal of the notion, consolidated over the early primary school years, that substances have an ongoing identity separate from the objects which represent their outer form, a concept of "material kind" (Dickinson, 1987). It involves abandoning the idea that substances necessarily have an ongoing identity through change m a transition from the belief that the products of burning are fundamentally the same materials (through a combination of modification, displacement, separation, and mixing) to a belief that the products should be considered as different substances, independent from their history. But as we have seen, this distinction is by no means a clean one to make. The question of whether we think of ash as a different substance to paper involves a question of what we think is important. As Johnson (I 997a) points out, the idea of defining substances by particular types of property is fundamental in chemistry, but not at all obvious to students. Which properties are of critical importance? Changing from a solid to a liquid, as with melting, is demonstrably not a fundamental change even though the properties are very different, since the solid form of the substance can be readily retrieved. But are there critical properties of the residue from a candle that it shares in common with the wax? Would a scientist be able to fred a critical property of the iron oxide residue that clearly marked it as an altered form of iron? For the children who were not sure what would happen if the residue was analysed, the question of whether it should be called a different substance was somewhat separate from the question of whether one could tell by analysing it what it's origin was.

A clear distinction between a modification and transformation view is only possible from a scientist's perspective, since it relies on an understanding of the primacy of properties, and ultimately on an understanding of atomic models of substances. For children without access to such ideas, the issue cannot be clearly defined. It is not legitimate to demand of them, for any given context, a clear modification or a transformation view. The fundamental change in conceptualizsation that is occurring relates to the more basic issue of whether students tend toward an explanation of changes to materials which is essentially historical, compared with an acceptance that new substances can be formed in a change process. These differ from the originals in terms of fundamental properties.

Figure 3 represents a model of conceptual progression in understandings of burning, and of changes to substances in general, arising from the above discussion.


Other models & associations:

Idea o f heat or flame as the source of new substances. Idea that the flame is the prior cause of change.

Initial conception of material kind: Substances have an ongoing identity separate

from the objects they comprise.

Conservation of substance: Change is conceived of as

displacement / mixing I separation of substances, and / or modification.

Transformation:

New substances arc formed in some types of changes to matter.

,L Rudimentary chemical reactions

view: Substances interact and reconfigure to make new substances with different

Chemical reactions view: Based on a particle model showing

the relationship of elements to compounds, new substances to old.

I Preservation of identity of materials, through physical change, becomes more confidently understood.

Idea of substance defined by their history gradually diminishes as instances of reformulation into new substances accumulate.

Increasing understanding of h o w substances can reformulate. Elements retain their integrity through chemical change, while substances do not.

Figure 3. A model of students' progression in conceptualisation of substance.

Posner, Strike, Hewson and Gerzog (1982), in their classic conceptual change model, include "plausibility" as one of the four requirements for accepting a new conception. Findings in this, and a related study (Tytler, 1997) indicate that an important factor in rendering the transformation conception plausible is the explicit identification of the products of burning, through attaching names to them. Alan seemed to find the naming of"soot" important for deciding it was a substance in its own right. The older children in particular seemed confident with the transformation idea related to the production of carbon dioxide. A full understanding of how these substances interact depends on distinguishing between elements and compounds as the two divisions of chemical substance, for which naming would seem an essential requirement.


Implications for Teaching and Learning

This study asked students to apply their ideas about combustion to a range of carefully framed, challenging phenomena, supported by group discussion. This represents as close to a teaching situation as can be experienced, without providing explicit input on scientific views of combustion. If one believes that successful teaching can only be built upon foundational ideas that students have access to, the study has implications for what can be taught effectively at different levels.

We have argued that the essential advance represented by a transformation view of chemical change involves the abandonment of the notion that substances have a continuing history, and that this idea starts to occur only in the upper years of primary school. This would imply that the proper focus of teaching of materials in the early and middle primary school years should be on physical change. Students in this study had access to the modification idea from an early age, supporting the current lower and middle primary school practice in dealing with changes to materials of emphasising changes of state (melting and freezing) and dissolving / mixing.

However, from the middle of the primary school years a distinction could be fruitfully drawn between changes where the substance retains its identity, and those where new substances are formed. Students need to be given explicit support in learning about those circumstances in which the historical integrity of substances is maintained, and those in which it is not. This discussion should emphasise properties of materials, and reversibility, as critical in developing a concept of substance.

We have argued that the naming of new substances is an important element in acceptance of the idea oflrausformation being accepted. Children's access to the chemical language of"oxygen" and "carbon dioxide," which seems to develop around Years 5 and 6, represents increased access to cultural understandings of substance that is possibly opened up by specific conceptual development as well as more general advances in language. This would seem to suggest the use, in the upper primary school, of technical language in talking about substances undergoing change. Perhaps referring to "carbon" as a product of disparate burning phenomena would be a useful strategy.

We believe that burning is a phenomenon that cannot be avoided in talking about changes to substances, and should be included in any sensible curriculum because of its social and personal relevance. Nevertheless, teachers need to be mindful of the difficulties it poses (Johnson, 199To) and should emphasise its commonality with other chemical change processes.

Correspondence: Dr. Russell Tytler, Faculty of Education, Deakin University, 221 Burwood Highway, Burwood, 3125, Australia. Intemet email: [email protected]

References

Adams, D., Doig, B., & Rosier, M. (1991). Science learning in Victorian schools: 1990. Hawthorn: Australian Council for Educational Research.

Andersson, B. (1986). Pupils' explanations of some aspects of chemical reactions. Science Education, 70(5), 549-563.

Andersson, B. (1990). Pupils' conceptions of matter and its transformations (age 12-16). Studies in Science Education, 18, 53-85.

BouJaoude, S. B. (1991). A study of the nature of students' understanding about the concept of burning. Journal of Research in Science Teaching, 28(8), 689-704.


Carey, S. (1985). Conceptual change in childhood, Cambridge, MA: MIT Press. Claxton, G. (1993). Minitheories: A preliminary model for learning science. In P. Black, & A.

Lucas (Eds.), Children's informal ideas in science (pp. 45-61). London, UK: Routledge. de Vos, W., & Verdonk, A. (1987). A new road to reactions: The substance and its molecules.

Journal of Chemical Education, 64, 692-694. Dickinson, D. (1987). The development of a concept of material kind. Science Education, 71(4),

615-628. diSessa, A. (1988). Knowledge in pieces. In G. Forman, & P. Pufall (Eds.), Constructivism in the

computer age (pp. 49-70). Hillsdale, N J: Lawrence Erlbaum and Associates. diSessa, A. (1993). Toward an epistemology of physics. Cognition and Instruction, 10(2&3), 105-

226. Driver, 1L, & Easley, J. (1978). Pupils and paradigms: A review of literature related to concept

development in adolescent science students. Studies in Science Education, 5, 61-84. Driver, R., (1985). Children "s ideas in science. Philadelphia, PA: Open University Press. Driver, R., Leach, J., Scott, P., & Wood-Robinson, C. (1994). Young peoples' understanding of

science concepts: Implication of cross-age studies for curriculum planning. Studies in Science Education, 24, 75-100.

Fensham, P. (1994). Beginning to teach chemistry. In P. Fensham, R. Gunstone, & R. White (Eds.), The content of science (pp. 14-28). London, UK: The Palmer Press.

Johnson, P. (1996). What is a substance? Education in Chemistry, 33, 41-42. Johnson, P. (1997a, January). Understanding chemical change: What does it take? Paper

presented at the annual conference of the Association for Science Education, Birmingham, UK.

Johnson, P. (1997b, September). Why combustion is one of the last things we should expect children to understand. Paper presented at the 4th European Conference on Research in Chemistry Education (ECRICE), York, UK.

Kmel, D., Watson, R., & Glazar, S. (1998). Survey of research related to the development of the concept of"matter." International Journal of Science Education, 20(3), 257-289.

Meheut, M., Saltiel, E., & Tiberghien, A. (1985). Pupils' (11-12 year olds) conceptions of combustion. European Journal of Science Education, 7(1), 83-93.

Osborne, R., & Cosgrove, M. (1983). Children's conceptions of the changes of state of water. Journal of Research in Science Teaching, 20(9), 825-838.

Pfundt, H. (1981). Pre-instructional conceptions about "substacnes and transformations of substances. In W. Jung, H. Pfundt, & C. yon Rhoneck (Eds.), Proceedings of the international workshop on problems concerning students" representation of physics and chemistry knowledge (pp. 320-341). Ludwigsburg.

Posner, G., Strike, K., Hewson, P., & Gertzog, W. (1982). Accommodation of a scientific conception: Toward a theory of conceptual change. Science Education, 66(2), 211-227.

Prieto, T., Watson, R., & Dillon, J. S. (1992). Pupils' understanding of combustion. Research in Science Education, 22, 331-340.

Ross, K. (1991). Burning: A constructive not a destructive process. School Science Review, 72(251), 39-49.

Schollum, B., & Happs, J. C. (1982). Learners' views about burning. The Australian Science Teachers' Journal, 28(3), 84-88.

Skamp, K. (1998, July). Atoms and molecules: Suitable content for Years 5 and 7? Paper presented at the annual meeting of the Australasian Science Education Research Association, Darwin.

Smith, C., Carey, S., & Wiser, M. (1985). On differentiation: A case study of the development of size, weight, and density. Cognition, 21, 177-237.


Stavridou, H., & Solomonidou, C. (1989). Physical phenomena-~hemical phenomena: Do pupils make a distinction? International Journal of Science Education, 11(1), 83-92.

Svensson, L. (1989). The conceptualisation of cases of physical motion. European Journal of Psychology of Education,/V(4), 529-545.

Tytler, 1L (1997, September). Teaching for conceptual change in science: Progression in primary school children's conception of matter. Paper presented at the biennal conference of the European Science Education Research Association, Rome, Italy.

Tytler, R. (1998a). The nature of students' informal science conceptions. International Journal of Science Education, 20(8), 901-927.

Tytler, R. (1998b). Children's conceptions of air pressure: Exploring the nature of conceptual change. International Journal of Science Education, 20(8), 929-958.

Watson, R., & Dillon, J. (1998). Progression in pupils' understanding of combustion. In G. Welford, J. Osborne, & P. Scott (Eds.), Research in science education in Europe (pp. 243- 253). London: Falmer Press.

White, R., & Gunstone, 1L (1992). Probing understanding. London, UK: Falmer.

Progression in primary school children's conceptions of burning: Toward an understanding of the...

Documents

Transcript of Progression in primary school children's conceptions of burning: Toward an understanding of the...