Vygotsky's sociocultural theory emphasized that cognitive development occurs through social interaction and language. According to Vygotsky, higher mental functions first appear on a social level through interaction with others and then on an individual level. He introduced the concept of the Zone of Proximal Development to describe the difference between what a child can do independently and with guidance and collaboration. Assisted learning through scaffolding helps children develop skills within their ZPD. Vygotsky also saw language as a critical tool that shapes thinking.