This document provides an overview of the cognitive development theories of Jean Piaget and Lev Vygotsky. Piaget was a Swiss psychologist who developed the theory of cognitive development occurring in stages that are age-appropriate. Vygotsky was a Russian psychologist who emphasized the social impacts on cognitive development and introduced concepts like the zone of proximal development. The thesis argues that Vygotsky's theory provides a more versatile foundation for schools today due to concepts like the zone of proximal development and its emphasis on societal influences on growth.