Social development theory was introduced in 1920s and 1930s by Lev Vygotsky. This theory gives a framework for cognitive development argues that the key role in cognition development lies in social interactions. In his own words, “every function in the child's cultural development appears twice: first, on the social level, and later, on the individual level; first, between people (interpsychological) and then inside the child (intrapsychological). This applies equally to voluntary attention, to logical memory, and to the formation of concepts. All the higher functions originate as actual relationships between individuals”¹⁾.

Vigotsky's theory addresses three main themes²⁾:

• Social interaction - which according to Vigotsky plays a crucial role in the process of cognitive development (and therefore learning precedes development), opposed to Jean Piaget’s stage theory of cognitive development where development precedes learning.
• The More Knowledgeable Other (MKO) - a term that addresses person (typically teacher or instructor, but others as well) or a machine that, when compared to the learner, has more knowledge and skills related to a particular task, process or concept
• The Zone of Proximal Development (ZPD) - a term to describe the zone between learners ability to complete a task with guidance or collaboration and ability to solve it alone. The ZPD is where learning occurs. Motivation for introduction of ZPD lies in observation that children could often accomplish tasks with the help of others that they could not accomplish alone.

The zone of proximal development is the difference between an individual's current level of development and his or her potential level of development. Full cognitive development requires social interaction.