Piaget's (1936) theory of cognitive development explains how a child constructs a mental model of the world.
He disagreed with the idea that intelligence was a fixed trait, and regarded cognitive development as a process which occurs due to biological maturation and interaction with the environment.
There are individual differences in the rate at which children progress through stages.
Piaget (1952) did not explicitly relate his theory to education, although later researchers have explained how features of Piaget's theory can be applied to teaching and learning.
Piaget (1936) was the first psychologist to make a systematic study of cognitive development.