On differentiation: a case study of the development of the concepts of size, weight, and density.

This paper presents a case study of 3to 9-year-old children's concepts of size, weight, density, matter, and material kind. Our goal was to examine two claims: (1) that individual concepts undergo differentiation during development; and (2) that young children's concepts are embedded in theory-like structures. To make progress on the first issue, we needed to specify in representational terms what an undifferentiated concept is like and in what sense this undifferentiated concept is a parent of the more differentiated concepts. Our strategy was to use a model of conceptual differentiation suggested by the history of science to guide our search for evidence. In this model, undifferentiated concepts, like differentiated concepts, can be analyzed in terms of their component properties, features, or dimensions. The key difference is that an undifferentiated concept unites certain components which will subsequently be analyzed as components of distinct concepts, and that the undifferentiated concept is embedded in a different theoretical structure from the differentiated concepts. In our study, the same group of 78 children (18 3-year-olds, 18 4-year-olds, 18 5-year-olds, 12 6-7-year-olds, and 12 8-9-year-olds) were given a range of tasks probing their understanding of size, weight, and density; a 'This research was funded by NSF Grant #SED-7913278, Joint NIE/NSF Research Program. We thank Renee Baillargeon, Ned Block , Rachel Falmagne, Arthur Millman, Helen Tager-Flusberg and two anonymous reviewers for their very careful reading of the manuscript and their many helpful suggestions for revisions. We also thank the teachers and children at the Cambridge Montessori School, Buckingham, Browne & Nichols School, Comer Co-op Nursery School. and Radcliffe Child Care Center for their participation in the study. David Dickinson, Denise LaBuda, Mara Levin and Phil O'Neil provided valuable research assistance. Reprint requests should be sent to: Carol Smith, Department of Psychology, University of Massachusetts/ Boston, Boston, MA 02125. U.S.A. 0010-02771851$18.80 © Elsevier Sequoia/Printed in The Netherlands