On differentiation: a case study of the development of the concepts of size, weight, and density.
D002648:Child; D002657:Child Development; D002675:Child, Preschool; D002755:Choice Behavior; D003210:Concept Formation; D006801:Humans; D008960:Models, Psychological; D012858:Size Perception; D014705:Verbal Behavior; D014892:Weight Perception