Piaget; Conservation

Piaget was one of the leading Constructivist theorist in Cognitive Development, his theory's are some of the most influential in his field. One of his most famous theories is the Conservation. The context of Conservation happens in the Preoperational Stage of Cognitive Development. Piaget noted that children in this stage do not yet understand concrete logic, cannot mentally manipulate information, and are unable to take the point of
view of other people, which he termed egocentrism.

This can be seen in this YouTube video on conservation.