Jean Piaget was a developmental psychologist who studied how children acquire knowledge. He believed that coercion was the worst teaching method and that children learn best through active participation and trial and error. Piaget provided a scientific basis for new teaching methods focused on examples and student participation, rather than experience or philosophy. He identified four stages of cognitive development from infancy to adulthood influenced by maturation, environmental interaction, social learning, and adapting through assimilation and accommodation.