The research of William Perry, the Harvard psychologist who documented cognitive growth in undergraduates, is summarized. Perry's theory is compared to Piaget's theory, and the view that Perry is an extension of Piaget is discussed. Also noted is the shift in locus of control and other measures that occur as students progress through Perry's positions. Perry researched transformations that occur during the college years regarding the perception of knowledge, and the culmination of his effort is a developmental model that reveals the sequence and nature of cognitive development and emotional maturation in undergraduates. The scheme of development is composed of a progression through nine stages. Three categories comprise Perry's scheme: dualism, multiplicity/relativism, and commitment. Since Perry's work is based on Piagetian theory, it is possible to see similarities. Both are stage theories, concerned with intellectual development, and have implications for instructional development. Perry's work is a departure from Piaget's because they use different methods and criteria and may actually be investigating different intellectual processes. As a stage theory, progression through Perry's scheme of development depends upon interaction between the environment and the cognitive processes of the student. Perry's search for the key to understanding the development of young adults goes beyond Piaget while using similar mechanisms. Further application of Perry's theory to learning style research must be done with the knowledge that the meaning and purpose of learning are dependent upon context and therefore the position of the student. Contains 8 references. (SM)