JOHN K. GILBERT MODELS AND MODELLING: ROUTES TO MORE AUTHENTIC SCIENCE EDUCATION1 ABSTRACT. It is argued that a central role for models and modelling would greatly increase the authenticity of the science curriculum. The range of ontological states available for the notion of ‘model’ is outlined, together with the modes available for their representation. Issues in the selection of models for and the development of modelling skills within the model-based curriculum are presented. It is suggested that learning within such a curriculum entails: acquiring an acceptable understanding of what a model is and how modelling takes place; having a developed capacity to mentally visualise models; understanding the natures of analogy and of metaphor, processes which are central to models and modelling. The emphases required in teaching for this learning to be supported are discussed. Finally, implications of the model-based curriculum for teacher education are evaluated. It is concluded that a great deal of detailed research and development will be needed if the potential of this change in emphasis within the science curriculum is to be realised. KEY WORDS: analogy and metaphor, authentic science education, learning models and modelling, model-based curriculum, models and modelling, teacher education for models and modelling, teaching models and modelling C URRENT C HALLENGES TO S CIENCE E DUCATION Many of those countries that currently aspire to achieve and retain prosperous economies place great value on the provision of science education for all citizens, not only during the years of schooling but also throughout life. The pattern of reactions by individuals to these national aspirations is mixed. In some countries the demand for science education is high, yet in others this is far from being the case. What is common across this spectrum of response is a feeling that science education currently faces a range of challenges. Students commonly find the subject – matter of science to be abstract, couched in complex language, and too often of insufficient immediate interest. This can lead to a lower than desired attainment in examinations and hence to a disinclination to continue the study of science beyond what is mandatory. The teaching of science requires a broad range of knowledge at some considerable depth of understanding, conditions often not supported by the ‘modular’ structures of courses provided by many uniInternational Journal of Science and Mathematics Education (2004) 2: 115–130 © National Science Council, Taiwan 2004 116 J.K. GILBERT versities. Given the high level of employability achieved by those with a background in science, good teachers are hard to recruit and retain in many countries. These problems in the learning and teaching of science have their roots in the nature of the science curriculum at all levels of educational systems. The curriculum can, in broad terms, be described as ‘sedimentary,’ meaning that information is continuously added to it, producing an incoherence of content and an excessive load of isolated ‘facts.’ This situation is made more demanding by the increasing insistence on ‘accountability’ by educational systems to government agencies, leading to an over-emphasis on an assessment of students’ knowledge of these facts. One way out of the conundrum facing science education is to make it much more ‘authentic:’ as closely alike the conduct of science per se as is possible under the current conditions of mass education. A more authentic science education would have a number of characteristics. First, it would more faithfully represent the processes by which science is conducted and its results are socially accepted: it should be more historically and philosophically valid. Second, it would reflect the core element of creativity that has made science one of the major cultural achievements of humanity in recent centuries. Third, it would provide a minimalist network of ideas with which to provide satisfactory explanations of phenomena in the world-as-experienced. Lastly, it would be capable of underpinning those technological solutions to human problems that are the basis of prosperous economies, social well-being, and the health of individuals. This paper suggests that models and modelling can form one basis for such a curriculum. M ODELS AND M ODELLING IN S CIENCE AND IN E DUCATION Models are essential to the production, dissemination, and acceptance, of scientific knowledge (Giere, 1988; Gilbert, 1991; Tomasi, 1988). Although their epistemological status is open to debate, they function as a bridge between scientific theory and the world-as-experienced (‘reality’). They can be simplified depictions of a reality-as-observed, produced for specific purposes, to which the abstractions of theory are then applied. They can also be idealisations of a possible reality, based on the abstractions of theory, produced so that comparisons with reality-as-observed can be made. They can be used to: make abstract entities visible (Francoeur, 1997); provide descriptions and/or simplifications of complex phenomena (Rouse & Morris, 1986); be the basis for both scientific explanations of and predictions about phenomena (Gilbert, Boulter & Rutherford, 1998). Both the design MODELS AND MODELLING 117 of and interpretation of experimental practices in modern science are often based on the use of computational modelling, Many models are of material objects and can be viewed as having an independent existence (e.g., a drawing of a reaction flask) or as being part of a system (e.g., a drawing of a reaction flask in an equipment train). A model can be smaller than the object that it represents (e.g., of an aeroplane) or larger than it (e.g., of virus). Some models are representations of abstractions, entities created so that they can be treated as objects (e.g., flows of energy as lines). Inevitably, a model can include representations both of abstractions and of the material objects on which they act at the same time (e.g., of energy flows in the Krebs’ cycle). A model can be of a system, a series of entities in a fixed relation to each other (e.g., of carbon atoms in a crystal of diamond, of the organs of the human body, of an electric motor). It can be of an event, a time-limited segment of behaviour of a system (e.g., of the migration of an ion across a semi-permeable membrane, of human gestation and birth). It can be of a process, in which one or more elements of a system are permanently changed (e.g., of a catalytic converter in operation). The central role of models in the development of knowledge was recognised by the mid-twentieth century (Bailer-Jones, 1999). For example, they have become ‘the dominant way of thinking’ in chemistry (Luisi & Thomas, 1990), something that chemists do ‘without having to analyse or even be aware of the mechanism of the process’ (Suckling, Suckling & Suckling, 1980). It therefore seems appropriate that models play equally important roles in science education. Students should come to understand the nature and significance of the models that played key roles in the development of particular themes in the sciences. They should also develop the capacity to produce, test, and evaluate models of those phenomena that are of interest to science. To do so is to participate in the creative aspect of science and to experience its cultural value. The roles of models in science education are not easy to discharge, for models can attain a wide diversity of ontological status. A mental model is a private and personal representation formed by an individual either alone or in a group. All students of chemistry must have a mental model, of some kind, of an ‘atom,’ all those of biology of a ‘virus,’ all those of physics of a ‘current of electricity.’ By its very nature, a mental model is inaccessible to others. However, a version of that model can be placed in the public domain and can therefore be called an expressed model. Any social group, for example, a school class, can agree on an (apparently!) common expressed model that therefore becomes a consensus model. A social group is of scientists working with a consensus model at the cutting 118 J.K. GILBERT edge of their science can be said to be using a scientific model, e.g., of a Schrödinger model of an atom, of a p-n junction in a semi-conductor, of the AIDS virus. A superseded scientific model can be called a historical model, e.g., the Bohr model of the atom, the Ohm’s law model of electrical conductance, the creationist model in biology. On major aspect of ‘learning science’ (Hodson, 1992) is the formation of mental and expressed models by individual students that are as close to scientific or historical models as is possible. Simplified versions of scientific or historical models may be produced as curricular models to aid learning (for example, the dot-andcross version of the Lewis–Kossel model of the atom). Specially developed teaching models are created to support the learning of curricular models (e.g., the analogy ‘the atom as the solar planetary system’) (Gilbert, Boulter & Elmer, 2000). Sometimes teachers employ curricular models which can be called hybrid models because they merge the characteristics of several historical models, this having first been recorded in respect of chemical kinetics (Justi & Gilbert, 1999). Whilst of immediate appeal to teachers, for they enable many ideas to be taught at the same time, they do violence to the history of science for they never existed in science and hence cannot ever be logically superseded. A further complication for science education is that any version of a model (i.e. an expressed, scientific, historical, curricular, or hybrid model) is placed in the public domain by use of one or more of five modes of representation. • The concrete (or material) mode is three-dimensional and made of resistant materials, e.g., a plastic ball-and-stick model of an ion lattice, a coloured plastic model of the human circulatory system, a metal model of an aeroplane. • The verbal mode can consist of a description of the entities and the relationships between them in a representation, e.g., of the natures of the balls and sticks in a ball-and-stick representation, of veins and arteries, of the parts of a model aeroplane. It can also consist of an exploration of the metaphors and analogies on which the model is based, e.g., ‘covalent bonding involves the sharing of electrons’ as differently represented by a stick in a ball-and-stick representation and in a space-filling representation. Both versions can be either spoken or written. • The symbolic mode consists of chemical symbols and formula, chemical equations, and mathematical expressions, particularly equations, e.g., the universal gas law, the reaction rate laws. • The visual mode makes use of graphs, diagrams, and animations. Two-dimensional representations of chemical structures (‘diagrams’) MODELS AND MODELLING 119 fall into this category as do the ‘virtual models’ produced by computer programmes. • Lastly, the gestural mode makes use of the body or its parts, e.g., the representation of the movement of ions during electrolysis by means of pupils moving in counter-flows. These canonical modes are often combined (Buckley, 2000), e.g., a verbal presentation of the visual representation of the Krebs’ cycle. If one approach to the provision of science education is to be through a much greater emphasis on models and modelling, consideration must be given the implications for curriculum design, for learning, for teaching, and for teacher education. As this approach, in an explicit form, has only recently begun to take shape, the discussion of these issues poses more questions than it provides answers. T HE I MPACT OF M ODELS AND M ODELLING ON C URRICULUM D ESIGN In the course of its evolution so far, science has produced a wealth of scientific and historical models. If the curriculum is to be made more coherent, it is necessary to select the most significant of these models for the curriculum. How is this to be done? One approach is through the identification of ‘key explanatory stories’ – those themes in science that have made the greatest contribution to our understanding of the natural world so far (Millar & Osborne, 2000). Examples of these stories are those about: chemical reaction; chemical bonding; the motion of the Earth; the formation, structure, and evolution of the Earth, the Solar System, the Universe; the action of forces; the causes of motion; the causes and direction of change; radiation and its interaction with matter (Millar & Osborne, 2000, p. 16). Each of these explanatory stories is built around one or more scientific/historical models. If an ‘explanatory story’ structure is ever adopted for the science curriculum, then the identification of the curriculum models involved will be straightforward. In the meantime, it is possible to reconceptualise existing curricula in terms of models. The science curriculum for pupils aged 5–16 years in the UK, originally laid down in 1988 (DfEE, 1999) on pragmatic grounds as a structure imposed on a collection of facts does, surprisingly enough, lent itself to an analysis in terms of models. The curriculum can be structured around curriculum models of ‘the particular nature of matter,’ ‘energy,’ ‘forces’ and ‘cells.’ This structure has been successfully implemented in schools in the south of England. 120 J.K. GILBERT For progression in their learning, pupils must encounter explanations that give both increased insight into the nature of particular phenomena and which can be used in respect of a increased range of phenomena. What does this mean for the models concerned? One approach might be through a successive introduction of the models in an historical sequence. An example is the sequence of models of acidity/alkalinity: • • • • • • • The Behavioural model (e.g., acids are ‘sharp’) – from antiquity. The Lavoisier model (acids as containing oxygen) – 1777. The Priestley model (acids as containing hydrogen) – 1777. The Arrhenius model (acids produce hydrogen ions in solution) – 1884. The Bronsted–Lowry model (acids as proton donors) – 1923. The Lewis model (acids as lone-pair acceptors) – 1923. The Usanovitch model (general solvent model) – 1939. (Oversby, 2000) Such an approach would only have educational value if it were taught with a genuine historicity. That is, in terms of a given model be able to provide certain explanations and being superseded when unable to provide explanations of new facts (Justi & Gilbert, 1999). Any science curriculum based on models and modelling must provide the opportunity for pupils to develop the capability to produce and test their own models. There is evidence that most current curricula offer little opportunity for his to take place (Justi, 2001; Justi & Gilbert, 2002). The process might take represented, if not take place, through a series of four discrete steps: Learning to Use of Models Here pupils apply a model in contexts where the outcome will be positive: that is, where it will successfully represent the chosen behaviour of a phenomenon. Arnold and Millar (1996) used a series of allied teaching models to introduce the notions of heat, temperature, thermal equilibrium to 12–13 year olds in the UK and, having done so, required them to apply these ideas to a range of other contexts. Halloun (1996, 1998) caused students to use scientific models in the solution of a range of paradigmatic problems in physics. Learning to Revise Models Model-revision is where pupils, having learnt how to use a model, have to change it in some way. The intention is that it can represent a phenomenon in contexts other than those initially encountered or so that it can be used for purposes other than originally envisaged. Stewart, Hafner, MODELS AND MODELLING 121 Johnson and Finkel (1992) taught the skills of model-revision by having high school students use a simulation of scientific activity. First, a phenomenon was observed in groups; that experience was then shared between the groups; then the groups each designed an explanatory model; the groups then defended their models against the critique of other groups; and finally the groups revised their models until a degree of convergence was achieved. This emergent skill of model-revision was then used on standard problems in genetics, using historical papers and computer software. The historical papers showed them how the problem had been solved at the time of the invention of the solution. The computer software enabled them to simulate the process of change of the explanation and the emergence of an acceptable solution. In an interesting variant of the model-revision theme, Frederiksen, White and Gutwil (1999) used computers to support students in progressing through (revising) a sequence of models of higher abstraction/complexity. Students were taken through a sequence of models of electricity (the electricity-particle model, the aggregation model, the algebraic model) such that the entities and interactions of a simpler model provided the emergent properties of the next in the sequence through a process of revision. Learning the Reconstruction of a Model This is where pupils are caused to create a model that they are aware exists but the details of which are unknown to them. Barab, Hay, Barnett and Keating (2000) had university students re-create the dynamic model of the solar system by the use of virtual-reality modelling tools. They were presented with a progressive series of questions, the more advanced of which required the construction and running of thought experiments and, later, pseudo-empirical experiments. They successively constructed a static model of the Earth–Sun system, a dynamic model of the Earth–Moon– Sun system, a dynamic model of the Solar system. Groups presented their work to each other. Finally, individuals wrote evaluations of the models produced and of how these related to the ‘standard model’ when it was shown them in detail. Learning to Construct Models de novo The MARS project (Raghaven & Glaser, 1995; Raghaven, Sartoris & Glaser, 1998a, 1998b) set out to develop model-building skills in grade 6 students in USA. Working on fundamental topics, e.g., ‘mass,’ ‘force,’ students did practical work, made predictions, inserted these predictions into a model constructed on a computer, ‘ran’ the model so produced to see how the outcomes compared with those produced by the consensus 122 J.K. GILBERT model. The long time scale needed for the development of modelling skills was noted, together with an improvement in the use of the explanation– prediction–evaluation sequence. The construction of a model de novo involves perceiving the emergence of properties of the complete model from those of the components of the model. Penner (2000) has discussed the issues involved and reported that this relationship cannot be established by grade 6 students. Exemplar sequences to take pupils through these four stages for particular models/phenomena have yet to be developed. The sequence does, of course, assume that the pupils have a good understanding of particular models (see later in this paper). L EARNING IN THE M ODEL -BASED C URRICULUM The only valid reason for teaching is to bring about learning. Thus, in considering the challenges to be faced in teaching the model-based curriculum, it is necessary to consider what successful learning in the field might entail. This may be divided, if only for convenience, into ‘having an acceptable understanding of what a model is,’ ‘having a developed capacity to mentally visualise models’ and ‘having an acceptable understanding of the natures of metaphor and analogy.’ Taking each of these in turn: The Nature of ‘Model’ In a pioneering study of Grosslight, Unger, Jay and Smith (1991) two ‘levels’ in school students’ understanding of the ‘nature of model’ were identified. Students in Level 1 thought of models as either toys or as copies of reality. Students in Level 2 thought of models as having been created for a purpose, with the emphasis on some components having been altered, but with the template of reality still predominating. A Level 3 was identified in ‘experts:’ educated adults with an interest in models. A Level 3 understanding accepted: that a model was created to test ideas (not as a copy of reality); that a model could be tested and changed in order to inform the development of ideas; and that a modeller had an active role in constructing a model, initially for a specific purpose. Confirmatory work based on this model has supported it, e.g., (Harrison & Treagust, 1996; Harrison & Treagust, 2000). Work inspired by the model has shown a similar distribution of ‘levels’ amongst secondary school science teachers (Van Driel & Verloop, 1999; Van Driel, Verloop & de Vos, 1998). In an interview-based study of 39 Brazilian science teachers from different phases of the education system (Justi & Gilbert, 2003) has identified four aspects to the notion of ‘model’ MODELS AND MODELLING 123 each of which contained several conceptions. These are its nature, what it is, the types of entities it represents, the use to which it can be put, and its stability over time. The issue for teachers is now how to support the attainment of an acceptable view of the ‘nature of model.’ The Capacity to Mentally Visualise Models There is general agreement that visualisation is an importance component in scientific achievement (Miller, 1987). Indeed, major advances often seem to be made by the use of ‘metaphorical imagination,’ a particular manifestation of visualization (Holton, 1995). The development of ‘visual literacy skills’ during the process of formal higher education – if not before that stage – has been advocated as being of central importance in the modern world (Christopherson, 1997). Such skills are thus of central importance in science education generally, and in chemical education (Tuckey & Selvaratnam, 1993) and earth science education (Piburn et al., 2002) especially. Achievement in chemical education in particular is closely linked to students’ skills of visualization (Coleman & Gotch, 1998). The terminology of the field lacks uniformity, with the term ‘visualization’ often being used to cover a range of spatial abilities. Barnea (2000) has analysed the terms ‘spatial ability’ or ‘visualization ability,’ often used interchangeably, into three skills in ascending order of importance: 1. Spatial visualization: the ability to understand accurately three-dimensional objects from two-dimensional representations of them; 2. Spatial orientation: the ability to imagine what a representation will look like from a different perspective; 3. Spatial relations: the ability to visualise the effect of operations such as rotation, reflection, and inversion, or to mentally manipulate objects. Despite, or perhaps because of, the complexity of the notion, and because of its central importance in chemical education, visualization must be treated as a metacognitive capability. Metacognition is ‘thinking about ones own thinking’ (Adey & Shayer, 1994) whilst a metacognitive learner is . . . one who understands the tasks of monitoring, integrating, and extending, their own learning. (Gunstone, 1994) A developed capability to think visually and to be able to think about the processes involved must be one of the goals of, if not a prerequisite for, science education. Again, the issue for teachers is how to develop that capability. 124 J.K. GILBERT The Nature of Metaphor and Analogy It can be argued that every new model is developed from an existing model (Lakoff & Johnson, 1980). The reduction ad absurdum aspect of this statement (i.e. where did the first model of a phenomenon come from?) offers wide scope for philosophical debate. The nature of and relationship between metaphor and analogy, the keys to the development of new models, is much disputed by linguists (Black, 1979). However, in broad terms, a metaphor is the temporary assumption that one thing is another thing. Thus ‘the sun is a furnace.’ The issue then is to decide the extent to which this identity is justified. Analogy is where a thing is said to be like another thing. An analysis of ‘the sun is like a furnace’ enables those aspects of a furnace that ‘map onto’ the sun to be used in a description of the latter. Hesse (1966) identified three aspects of any ‘source’ (e.g., a furnace) that is used to describe the target (e.g., ‘the sun’). There is the positive analog, which could properly be used in the analogy (the model). There is the negative analog, which could not be used in the model. And, perplexing for all students, the neutral analog, where it was not clear whether those parts can be ‘translated’ into the model or not. Metaphor and analogy sit within the complex of the verbal linguistic devices used in science and elsewhere. The verbal mode can be the presentation of the model as a structure in its own right i.e. a description of the entities of which it is thought to consist and of the relationships between them. However, it is often the case that a verbal presentation seeks to explain the model i.e. to show how and why it was produced. This latter type of verbal presentation is thus concerned with the identification of similarities between something that is already understood and something that has to be understood with the use of analogy. However, ‘similarity’ is TABLE I Type of similarity Entities transferred from source to model Relationships transferred from source of model Example Mere appearance Yes No Literal similarity Analogy Abstraction Yes No No Yes Yes Yes A glass tabletop gleamed like a pool of water. Milk is like water. Heat is like water. Heat is a through-variable. MODELS AND MODELLING 125 a somewhat slippery concept, for (Gentner, 1983, 1988, 1989) identified four variants, illustrated in Table I. To be able to discuss models and to engage in modelling, students must understand the nature of analogy at the ‘abstraction’ level. Another major task for teachers thus is to support the attainment and use of this level of understanding of ‘analogy.’ T EACHING THE M ODEL -BASED C URRICULUM Teaching must, therefore, support the development of these three types of capability in their students. Again, taking each in turn: The Nature of Model One obvious way to develop both students’ understanding of the nature of ‘model’ is to give them first-hand experience with a wide range of modes and sub-modes of representation of models. This has its problems. Students can prefer simpler models, even when they know more advanced models, e.g., of ionic bonding (Coll & Treagust, 2001). They can fail to appreciate the scope and limitations of the different modes/sub-modes of representation (Ingham & Gilbert, 1991). They can place greater reliance on the material/concrete mode than on other modes (Harrison & Treagust, 1996). These problems can be addressed by using a mixture of instruction about the utility of different models available in a field of enquiry, about the conventions of interpretation and hence the scope/limitations of the modes/sub-modes of representation used. This instruction should be combined with the direct use by the students of a range of modes/sub-modes to actually construct representations. The advent of computer-managed modelling packages in recent years has added greatly to the repertoire of scientists in these respects, especially for chemists (Mainzer, 1999) and chemical educators (Ealy, 1999). These packages enable representations of exemplars of the phenomenon itself (via video), dynamic representations in virtual (or pseudo-) 3D of material mode representations, conventional 2D representations (diagrams), representations in the mathematical mode (including chemical equations), to be created, juxtaposed, manipulated, and hence discussed. There is evidence of their success in developing the notion of model (Kosma, Chin, Russell & Marx, 2000; Treagust & Chittleborough, 2001). Their use is thus expanding rapidly. 126 J.K. GILBERT The Capacity to Visualize Models The skills of visualization do improve with age during childhood and adolescence, with relevant experience playing a major role in that development (Tuckey & Selvaratnam, 1993). Studies of gender and visualization seem inconclusive: any possible initial advantage for boys can readily be nullified by suitable experience for girls (Tuckey & Selvaratnam, 1993). Experience of the combination of concrete molecular models and pseudo-3D computer-based modelling tools has been shown to enable school science students to move more readily both between 2D and 3D representations (Dori & Barak, 2001). However, such attempts to combine experience across modes seem to be comparatively rare. More develop work, associate with research, is called for. The Nature of Metaphor and Analogy Support by teachers in developing a suitable understanding of metaphor and analogy is undoubtedly needed. We must turn to our colleagues in First Language (so-called ‘Mother Tongue’) for ideas on how to do this. Better still, we should bring pressure to bear on teachers of language to do this on behalf of science education. T EACHER E DUCATION The recognition of the roles of models and modelling in science education is a fairly recent event. Consequently, science teachers today have often not been explicitly educated and trained in the theme. In order to introduce and sustain a more authentic, model-based curriculum, and to guide students in their learning, science teachers need a wide range of types of specific knowledge and skill (Shulman, 1987). Thus: 1. Teachers’ knowledge of their subject, their ‘subject content knowledge,’ must include a comprehensive understanding of ‘curriculum models:’ those simplified versions of scientific/historical models that are mandated for teaching. This knowledge will include an understanding of the entities of which the models are constructed and of the nature of the cause-effect relationships operating within them. It is especially important that teachers understand the scope and limitations of each of these models: the purposes to which they can be put and the quality of the explanations to which they can give rise. Although not dealt with in this paper, such understanding cannot be taken for granted, given the widespread occurrence of misconceptions of all kinds amongst teachers. See, for example, (Gilbert & Watts, 1983). MODELS AND MODELLING 127 2. Teachers’ curricular knowledge should include when, how, and why the general idea of modelling and models, together with the details of specific scientific/historical models, should be introduced into the curriculum and into schemes of work. In other words, teachers should be able to select, develop and/or change, existing curricular models related to the topics to be taught at specific grade levels. 3. Teachers’ pedagogical content knowledge should include their ability to develop good teaching models, analogues for particular intellectually demanding curricular models that are used to support the learning of the latter (see, for example, Treagust & Chittleborough, 2001; Treagust, Harrison, Venville & Dagher, 1996). They must also be able to conduct modelling activities, understand how their students construct their own mental models; and be able to deal appropriately with the resulting models when expressed in class (Gilbert & Boulter, 1998). 4. Teachers’ subject content knowledge should include a comprehensive understanding of the nature of what a model is. This would include aspects such as, for instance, the use to which a model can be put, the entities which a model may represent, the factors that govern the retention of a given model in science over long periods of time (Justi & Gilbert, 2002). This understanding must underpin all the other requirements of teachers in respect of models and modelling, outlined above. The demands that these requirements place on teacher education are considerable and, in my view, must be explicitly addressed. 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