Jean Piaget was a Swiss psychologist whose research on the development of children has profoundly affected psychological theories of development and of the teaching of children. His theory has also been widely studied for its application to the teaching of science in grade school, high school, and college. Piaget's theory conceives of intellectual development as occurring in four distinct periods of stages. Intellectual development is continuous, but the intellectual operations in the different periods are distinctly different.
Children progress through the four periods in the same order, but at very different rates.
The stages do not end abruptly but tend to trail off. A child may be in two different stages in different areas. In this period a child learns about his or her relationship to various objects. This period includes learning a variety of fundamental movements and perceptual activities. Knowledge involves the ability to manipulate objects such as holding a bottle.