Jean Piaget (1896–1980) was a Swiss psychologist who produced an extremely influential body of work on the intellectual development of children. Unlike Freud and Erikson, who developed comprehensive theories about personality development in children, Piaget had a more narrow focus. He was exclusively interested in the child’s intellectual development. He wanted to understand the ways that children learn to understand their environment. It was Piaget’s brilliant insight to recognize that children do not only differ from adults in the content of their knowledge; they also differ in the structure of their knowledge. They not only know less, they know differently.

Piaget proposed four stages of intellectual (or cognitive) development: sensory-motor, pre-operational, concrete operational, and formal operational. Although Piaget failed to consider the important roles of culture, language, or environment on cognitive development, his basic ideas maintain their tremendous importance and influence, particularly in the field of educational psychology.