Zone of Proximal Development (ZPD) was introduced by:

The concept of the Zone of Proximal Development (ZPD) was introduced by the prominent Soviet psychologist Lev Vygotsky. Vygotsky's sociocultural theory emphasizes the role of social interaction and culture in cognitive development. The ZPD defines the space between what a learner can achieve independently and what they can accomplish with the guidance and support of a more knowledgeable other, such as a teacher or a more skilled peer. Vygotsky posited that learning is most effective when instruction is targeted within this zone, using 'scaffolding' to help learners bridge the gap between their current and potential abilities.

• Jean Piaget, while a highly influential figure in cognitive development, focused on stages of individual cognitive development and the child's active construction of knowledge through interaction with their environment, rather than the ZPD.
• B.F. Skinner was a leading proponent of behaviorism, primarily known for his work on operant conditioning, which explains learning through reinforcement and punishment. His theories do not include the ZPD.
• Edward Thorndike was another significant psychologist known for his work on the 'law of effect' and instrumental conditioning, which laid foundational principles for behaviorism. His theories predate and differ significantly from Vygotsky's sociocultural approach and the ZPD.