Abstract
A developmental study of free-classification behavior within the age range of 3-1/2 to 19 years indicates that categorical responses, which are characteristic of adult behavior, increase with age while overgeneralized responses, classifications including noncategorical instances, decrease with age. Overdiscriminated responses which are incomplete categorical classifications increase from 3-1/2 to 6 years and then decrease to 19 years of age. These results are discussed within a two-stage theory of conceptual development (Kendler, 1971).