Modelling in science lessons: Are there better ways to learn with models?

School Science and Mathematics, Dec 1998 by Harrison, Allan G, Treagust, David F

A Typology of Concept-building Analogical Models

Concrete and Concrete/Abstract Models Designed to Represent Reality

Scale models. Scale models of animals, plants, cars, and boats are often used to depict colors, external shape, and structure. Such models carefully reflect external proportions but rarely show internal structure, functions, and use, nor are they made of the same materials as the target. Also, size-for-size, a scale model bridge is stronger than the actual bridge (Hewitt, 1987, pp. 259-263)! Teachers need to highlight this difference and the unshared attributes of scale models, because scale models look so realistic.

Pedagogical analogical models. These are the concrete models that teachers often use to depict abstract or nonobserveable entities like atoms and molecules. One or more target attributes dominate the analog's concrete structure; e.g., ball-and-stick and space-filling molecular models, or a simple tube representing an earthworm's gut (Ogborn et al., 1996). Because these analogical models reflect point-bypoint correspondences between the analog and the target for a limited set of attributes, they can be grossly oversimplified to highlight conceptual attributes. Such oversimplifications should be carefully discussed with the students.

Abstract Models Designed to Communicate Theory Iconic and symbolic models. Chemical formulae and chemical equations are symbolic models of compound composition and chemical reactions, respectively. Formulae and equations are so embedded in chemistry's language that school students and nonspecialist teachers mistake them for reality when they are, in fact, explanatory and communicative models.

Mathematical models. Physical properties, changes, and processes (e.g., k = PV, F = ma), can be represented as mathematical equations and graphs that elegantly depict conceptual relationships (e.g., Boyle's Law, exponential decays, etc.). However, F = ma only functions in frictionless situations, which never exist in classrooms; therefore, the ideal nature of these models should always be discussed with students. It is also important that students construct, for themselves, qualitative explanations for these mathematical models. Theoretical models. Analogical representations of electromagnetic lines of force and photons are theoretical, because the models are human constructions describing well-grounded theoretical entities. Theoreti.cal explanations, like the kinetic theory model of gas volume, temperature, and pressure, belong to this category. Also, simplifying kinetic theory particles as spheres qualifies them as pedagogical analogical models. Some phenomena may belong to, or contain, both theoretical and mathematical models. Whenever possible, then, students and teachers should negotiate qualitative explanations of theoretical models. Models Depicting Multiple Concepts and/or Processes Maps, diagrams, and tables. These models represent patterns, pathways, and relationships easily visualized by students. Examples are the periodic table, phylogenetic trees, weather maps, circuit diagrams, metabolic pathways, blood circulation, nervous systems, pedigrees, food chains, webs, and pyramids. Note that the simplified and enhanced nature of parts of these diagrams make them two-dimensional models, and individual students interpret diagram items and colors in different ways.