While Jean Piaget's work as it relates to the development of childhood and adolescent cognition has long been explored, only recently has the usefulness of Piaget's theory in the study of adult cognition been studied. Recent research by educational psychologists has raised serious doubts about Piaget's theoretical position that the highest level of cognition or formal operational thought is achieved by adolescence and maintained as static over life-span. John Flavell, a leading interpreter of Piaget, has suggested that adult cognitive changes, unlike childhoold cognitive development, which is based on biological events, have their source in experience. Differences in rate and intensity of cognitive development in adulthood result from varying experiences with various degrees of intensity for adults. Evidence from studies of college students has challenged the theory that the final stage of cognitive development is fully achieved at adolescence. Researchers have also investigated the phenomenon of reverse decalage in older persons (a suggestion that formal operations among the elderly follow a pattern of decline in the same order in which they were acquired in the early years). Studies in this area have yielded conflicting results. (YLB)