A discussion of models of intellectual development and their application to education identifies the two major groups of such models and examines recent attempts to combine them. The two types of theories are described as the psychometric models, which see intellectual growth as the incremental amassing and associating of discrete ideas, and the structuralist or growth stage models, which view growth as a "stage-wise" series of qualitative transformations or reorganizations of the intellectual and affective processes. The authors first review the psychometric models, noting their orientation toward tests of vocabulary and other abilities as well as their lack of a theory of growth. The paper then considers the insights and problems produced by the growth stage models. It touches on the functional-descriptive models of Gesell and Havighurst, the psychoanalytic stage models of Freud and Erikson, and Piaget's cognitive development model. The paper's final sections discuss recent attempts to reconcile psychometric models with the cognitive development theory, including structural behavioralism and neo-Piagetian theory. These recent theories, observe the authors, may offer new ways to apply development theory to education. (RW)