Conservation refers to an ability in logical thinking according to the psychologist Jean Piaget who developed four stages in cognitive development. By the third stage, the Concrete operational stage, the child of age 7-11 has mastered this ability, to logically determine that a certain quantity will remain the same despite adjustment of the container, shape, or apparent size.

Piaget's tests with young children analysing their ability to conserve were criticised by Samuel and Bryant, who performed a partial replication of his original experiment in order to test the reliability of the results. They found that Piaget's methodology may well have produced some of the results he stated, but also that cognitive development is in fact age related.

This study is used in A-level psychology

Developmental psychology | Psychological theories