Jean Piaget was a Swiss psychologist born in 1896 who studied cognitive development in children. He is known for developing the theory of four cognitive development stages: sensorimotor, preoperational, concrete operational, and formal operational. The stages describe the typical development process from birth through adulthood in how children and adolescents understand and reason about the physical and social world. Piaget believed that education should focus on helping students develop new ways of thinking rather than just repeating old knowledge.