Lev Vygotsky was a Soviet psychologist who developed the theory of social development. He believed that social interactions and culture strongly influence child development. According to Vygotsky, learning occurs first on an interpersonal level through interactions with others, then on an intrapersonal level as children internalize knowledge. The theory emphasizes the role of the More Knowledgeable Other and the Zone of Proximal Development in guiding learning. Teachers can support student development by structuring social interactions and guidance within students' ZPDs, including with technology.