Summary: Social Development Theory argues that social interaction precedes development; consciousness and cognition are the end product of socialization and social behavior. Originator: Lev Vygotsky (1896-1934). Key terms: Zone of Proximal Development (ZPD), More Knowledgeable Other (MKO) Vygotsky’s Social Development Theory Vygotsky’s Social Development Theory is the work of Russian psychologist Lev Vygotsky (1896-1934), who lived during Russian Revolution. Vygotsky’s work was largely unkown to the West until it was published in 1962. Vygotsky’s theory is one of the foundations of constructivism. It asserts three major themes: Major themes: