Without a doubt, Piagetian theory puts forward an approach that has had a fundamental impact on today’s developmental psychology. There has been an appropriation—explicit or just more or less implicit—of essential theoretical assumptions of Piaget, such as the assumptions that development occurs in stages and structures underlie behavior. Piaget’s empirical findings have triggered off numerous attempts at replication. And there have been countless cases in which the tasks for determining different levels of structure sketched out by him have been used to investigate other aspects of cognitive development—within the framework of other approaches, such as information-processing models. Furthermore, modified and even alternative approaches have been developed through a direct confrontation with the Piagetian theory.