The developmental theory of Jean Piaget describes intellectual growth, from sensorimotor intelligence through adult logic. Although Piaget has not dealt with mentally retarded (MR) persons per se, his theory has been applied to that population by many researchers. Results of investigations into this application of Paget's stage theory of development indicate that the stages of development in the MR parallel those described by Piaget but appear at later chronological periods. Because of the tremendous variability in cognitive MR task performance within IQ categories, identification of specific aspects of concept learning holds promise for enhancing the school performance of MR children through individualized instruction.The developmental theory of Jean Piaget deals with the process of intellectual development. The theory focuses on the evolution of abstract thinking from its origins in the sensorimotor behavior of infancy through the intermediate forms (Woodward, 1963). Piaget is not concerned with success or failure, right or wrong, but rather with the kinds of psychological operations comprising intellectual development. His purpose is not to make an inventory of behavior; it is to interpret behavior in terms of its origins and to predict what will grow from it at successive stages.Piaget suggests that the central nervous system, as a result of its interaction with the environment during the early years, &dquo;constantly forms levels of integration which are both quantitatively and qualitatively different from the synthesis out of which they evolved&dquo; (Robinson & Robinson, 1965, p. 356). Moreover, his conceptions of psychological development are very different from those generally espoused by theorists who view learning mainly in terms of an associationist model; thus, they have far-reaching ramifications for the study of nearly every area of child development.The phenomenon of mental retardation poses many questions of critical importance conerning both the universality and the individuality of mental development (Kessler, 1970). The study of this phenomenon from the perspective of Piagetian theory offers promise of increased understanding -both of mental subnormality and of the processes and sequences of mental development. Therefore, the purpose of this review is to analyze some of the major areas in