Lev Vygotsky's sociocultural theory posits that cognitive development occurs through social interaction and language. According to the theory, learning is mediated by others and mediated tools shape mental development. A key concept is the Zone of Proximal Development, defined as the difference between what a learner can do independently versus with guidance. Scaffolding, where a more knowledgeable person provides support, enables learning within the ZPD. The theory emphasizes social learning preceding development and has implications for collaborative, scaffolded instruction.