Jean Piaget (1896–1980) was a Swiss developmental psychologist whose work on cognitive development transformed the study of how children learn. His central insight — that children are not passive recipients of knowledge but active constructors of understanding — became foundational to constructivism in education.
Piaget described cognitive development as proceeding through stages (sensorimotor, preoperational, concrete operational, formal operational), each characterized by qualitatively different modes of reasoning. While the strict stage model has been revised by subsequent research, his core claim — that learners build understanding by integrating new information with existing mental structures — remains widely influential.