The study of andragogy, a well developed science in Europe, is gaining greater acceptance in the United States. Malcolm Knowles introduced it to American adult educators in 1968 and has made it the central theme of his work since. The distinction between andragogy (the art and science of helping adults learn) and pedagogy (the art and science of teaching children) is basic to an understanding of andragogical theory. Andragogical learning is self-directed; pedagogical is teacher-directed. The learner's experience is seen as a rich resource for learning, readiness develops from life tasks and problems (not dependent on maturation levels), orientation is task or problem-centered (rather than concept-centered), and motivation is based on internal incentives (rather than external rewards). Combining elements from humanist psychology and a systems approach to learning, andragogy has its theoretical and philosophical bases in the work of John Dewey, E. H. Erikson, Jerome Bruner, Abraham Maslow, and Carl Rogers. Several recent theorists and researchers have reflected on the failure of "traditional" secondary schools in relationship to the concept of the adolescent as an evolving adult capable of engaging the andragogical process (a concept supported by Piaget's theory of adolescent learning). Others, noting the UNESCO conceptual model of lifelong learning with its basis in Dewey and andragogical theory, have identified "untenable" assumptions underlying education systems; these may be viewed as largely characteristics of the traditional pedagogical model. (JT)