A pioneer for cognitive theory and developmental psychology.
Piaget had a theory about cognitive development stages in children. He believed in four stages of development, known as schema, which began at infancy and went into adulthood. The stages, in order of youngest to oldest, are sensorimotor, preoperational, concrete operational, and formal operational.
Cognitive Development: the process of inquiring intelligence and increasingly advanced thought and problem-solving ability from infancy to adulthood
"To express the same idea in still another way, I think that human knowledge is essentially active." -Jean Piaget