Radical and Social Constructivism
Constructivist ideas fall into a couple of not-always-distinct camps. The first camp, which finds its extreme expression in the radical constructivism of Ernst von Glaserfeld, revolves around the idea that each individual constructs reality for him or herself. Radical Constructivism puts forward two main claims (von Glasersfeld 1989: 162):
"(a) knowledge is not passively received but actively built up by the cognizing subject;
(b) the function of cognition is adaptive and serves the organization of the experiential world, not the discovery of ontological reality."
In other words, all experience is subjective, filtered through the prism of individual biases, experiences, and sense perceptions. The mind simply organizes this stuff into something we call "reality."
An alternate camp, generally referred to as social constructivism, emphasizes the role of culture and context in developing personal and shared interpretations of reality. It emerges largely from the work of Piaget, Vygotsky, Bruner, and Bandura. It shares with radical constructivism the idea that reality is constructed, but to social constructivists this construction does not exist prior to its social invention. Knowledge is a social product, and learning a social process, and meaning is an agreement shaped by social patterns and the assumptions encapsulated in language.
One particularly influential social constructivist-based theory is Vygotsky's idea of the Zone of Proximal Development. The ZPD describes the difference between what a person can learn on his or her own, and what that person can learn when learning is facilitiated by someone with greater expertise. The idea of well-timed instructional interventions, operating within an individual's ZPD, has become stock-in-trade for instructional design models ranging from the whole-language approach to learning reading and writing, to various methods for training individuals within a corporate culture.
Social constructivism is related to the concept of situativity, which is discussed separately.
Glasersfeld, Ernst von (1989) Constructivism in Education. In: T.Husen and T. Neville Postlethwaite (eds) The International Encyclopedia of Education. Research and Studies, pp. 162-163. Supplementary Volume 1. Oxford: Pergamon Press.