Students' spontaneous use of a particulate model for dissolution

In this phenomenographic study of dissolution, data were drawn from 217 students aged 12 to 14 years, representing a wide ability range. Some were whole Year 9 classes in non-selective schools near London, while 150 were isolated, randomly selected subjects from the TIMSS (Third International Mathematics and Science Study) in the UK. All respondents watched or performed the dissolution of a solid in both cold and warm water, and then wrote their explanations. Analysis yielded an estimate of the frequency of un-cued deployment of particulate models. The wide range of alternative conceptions is discussed in terms of use of analogy, association of ideas, the vernacular language, and selective observation. On an inexact estimate, approaching half of all the responses had merit as explanations, although less than half of these made use of the particulate model. These findings have implications for the teaching of all science theory, but especially for conveying the purpose of models, and the process of modelling.