ABSTRACT
The study of development normally presupposes an understanding of the fully developed individual. In normative studies, adult structure dictates the variables that developmentalists must attend to: A theory of language acquisition, for example, must be able to account for the mastery of grammatical rules that competent adult speakers show. In studies of individual differences, adult status is the ultimate criterion that developmental variables must predict: Adult vocabulary scores might be the outcome in a study of educational enrichment.
