Constructivism is divided into two major schools of thought: cognitive constructivism and social constructivism. Cognitive constructivism is based upon the work of Dewey (1938), Bruner (1966), and Piaget (1972). This theory revolves around the concept that learners construct their knowledge through individual personal experiences. Social exchange and collaboration are foci of the social constructivist theory grounded in the work of Vygotsky (1978). A major theme of social constructivist theory is that social interaction plays a fundamental role in the development of cognition. Vygotsky postulated that cultural development happens twice, first on the social level (between people), then later on the individual level (inside the mind). An important contribution of social constructivism is the idea of the Zone of Proximal Development (ZPD) defined as the space between what a learner can do without assistance and what a learner can do with adult guidance or in collaboration with more capable peers. Learners can be pushed beyond their existing capabilities with external support or “scaffolding.” As learners become more accomplished, the amount of scaffolding is reduced or “faded.”