| The construction of the concepts of material kind, solid and liquid, and the development of children's theories of burning, rotting, and rusting (i.e., "material-based processes") were investigated. Subjects at five ages, four, six, nine, and twelve years old, and adults, were interviewed using structured interviews. There were twenty-two subjects among the six and nine year old groups, and ten subjects in the other groups. The interviews included sorting of materials, demonstrations, and open-ended questions.;Four year olds were unable reliably to distinguish material kinds from objects; they had some success predicting the behaviors of solids and liquids, but they could not sort items as "solids" and "liquids"; and they failed to consider material kind when predicting material-based processes. Six and nine year olds were able to sort by material kind, but they believed kind was altered by grinding and melting bulk solids. When sorting materials and liquids and solids they confused use of phase features (e.g., shape) with material kind features (e.g., density). Their theories of material-based processes reflected developing awareness of material kind and lingering confusion between phase and material kind. Seventh graders knew that material kind was unaffected by gross physical transformations, and they began to distinguish more clearly phase and material kind and to make appropriate use of knowledge about materials when considering material-based processes. Adults continued the trends toward differentiation observed at seventh grade. The differentiations observed were interpreted as reflecting both increased knowledge about materials and knowledge of more powerful scientific theories (e.g., atomic theory).;The research revealed the need to study related systems of concepts in order to discover the development of particular concepts. The development of these fundamental, but previously neglected concepts is of interest to science educators and developmental psychologists; additional research is needed to refine and replicate the findings reported.;It was hypothesized that children would initially have difficulty differentiating important concepts: functional object (e.g., spoon, airplane) from material kind (e.g., plastic, wood), and material kind from phase (e.g., solid, liquid). The progressive differentiation of these concepts was expected to occur in the context of the development of systems of concepts (i.e., theories). The conceptual confusions were expected to be reflected in children's understanding of material-based processes. |
