Jean Piaget is one of the major proponents of developmental theories and his work has had a significant impact in the world of developmental psychology. Thus, many others have built on his ideas, utilizing his thoughts to conduct further research on development and intelligence.
His theory of cognitive development deals with the issue of human intelligence and knowledge and how as humans, we come to acquire this necessary element of life. To do this then, he divides development into four basic stages: sensorimotor, preoperational, concrete operational, and formal operational. The stages encompass a person’s entire life, with the sensorimotor stage beginning at birth, the formal operational beginning at around 11 years of age, and ending with adolescence.