In a nutshell, the absorption of knowledge from context, being knowledge in the sense of ‘knowing how’ rather than ‘knowing that’ [according to the well-worn distinction made by Gilbert Ryle (1900-1976) in his book the Concept of mind, 1949]. For Lev Vygotsky (1896-1934), it was a cardinal concept in his sociocultural theory (the others being semiotic mediation and the zone of proximal development) and his attempt to show the interrelationships between language and thought developed. Accordingly, internalization involves the gradual transformation of social phenomena into psychological phenomena through interactions between children and those with whom they have regular contact, initially parents but increasingly so classmates and friends. The hallmark of this transformation is internal speech and its differentiation (or appropriation) from social speech. This external (social)-internal (psychological) distinction is captured in a frequently cited quotation from Vygotsky’s book Thought and language (1981): “Any function in a child’s cultural development appears twice on or on two planes. First it appears on the social plane and then on the internal plane. First it appears between people and as interpsychological category, and then as within the child as intrapsychological category (p. 163)”. The process of internalization portrayed by Vygotsky was diametrically opposed to Piaget’s vision of genetic epistemology (at least in its original formulation). This contrast is captured by Barbara Rogoff in her book Apprenticeship in thinking (1990) by pointing out that Piaget’s image of “the child as a scientist’ is replaced by ‘the child an apprentice’ in Vygotsky’s theory.
See Action theory, Context (cultural), Developmental epistemology, Instruction, Internal speech, Zone of proximal development