1. Constructivism
Constructivism — particularly in its "social" forms — suggests that the learner is much more actively involved in a joint enterprise with the teacher of creating ("constructing") new meanings. It is the importance of culture and context in forming understanding.
Learning is not a purely internal process, nor is it a passive shaping of behaviours. Vygotsky favoured a concept of learning as a “social construct which is mediated by language via social discourse.” (McMahon, 1997)
Laurillard emphasises learning as an iterative process, involving discursive, adaptive, interactive, and reflexive qualities, the main focus being on teacher-student relationship since "academic knowledge consists in descriptions of the world, and therefore comes to be known through a discursive interaction between teacher and student".
Traditional behaviourist/instructivist approaches strive for context independence, whereas a Social Constructivist paradigm views the context in which the learning occurs as central to the learning itself.
One Social Constructivist notion is that of authentic or "situated learning", where the student takes part in activities which are directly relevant to the application of learning and which take place within a culture similar to the applied setting.

2. Cognitive and Social Constructivism
We can distinguish between
"cognitive constructivism" which is about how the individual learner understands things, in terms of developmental stages and learning styles, and
"social constructivism", which emphasises how meanings and understandings grow out of social encounters (Vygotsky)

3. Vygotsky
The most significant bases of a social constructivist theory were laid down by Vygotsky [ ] (1962):
The ability to think and reason by and for ourselves (inner speech / verbal thought) is the result of a fundamentally social process.
At birth, we are social beings, capable of interacting with others, but able to do little either practically or intellectually, by or for ourselves.
Gradually, however, we move towards self-sufficiency and independence, and by participating in social activities, our abilities become transformed.
For Vygotsky, cognitive development involves an active internalisation of problem solving processes that takes place as a result of mutual interaction between children and those with whom we have regular contact (initially parents and later friends and class mates).

4. Scaffolding
Scaffolding refers to the role played by parents, teachers and others by which children acquire their knowledge and skills (Wood et al, 1976).
As a task becomes more familiar to the child and more within its competence, so those who provide the scaffold leave more and more for the child to do until it can perform the task successfully.
In this way, the developing thinker does not have to create cognition ‘from scratch’: there are others available who have already ‘served’ their apprenticeship.

5. Zone of Proximal Development
The theory of the "Zone of Proximal Development" (ZPD) is a term coined by Vygotsky to refer to the:
‘level of potential development as determined through problem solving under adult guidance or in collaboration with more capable peers…..What children can do with the assistance of others might be in some sense even more indicative of their mental development than what they can do alone’ (Vygotsky, 1978).
"Proximal" simply means "next". He observed that when children were tested on tasks on their own, they rarely did as well as when they were working in collaboration with an adult. It was by no means always the case that the adult was teaching them how to perform the task, but that the process of engagement with the adult enabled them to refine their thinking or their performance to make it more effective. Hence, for him, the development of language and articulation of ideas was central to learning and development.  The common-sense idea which fits most closely with this model is that of "stretching" learners.

6. ZPD
Vygotsky claimed that all developing individuals have both an actual developmental level and a ZPD. A difference exists between what a child can do on her own and what the child can do with help. Vygotskians call this difference the zone of proximal development.

7. How Vygotsky Impacts Learning:
Curriculum - Since children learn much through interaction, curricula should be designed to emphasize interaction between learners and learning tasks.
Instruction - With appropriate adult help, children can often perform tasks that they are incapable of completing on their own. With this in mind, scaffolding - where the adult continually adjusts the level of his or her help in response to the child's level of performance is an effective form of teaching. Scaffolding not only produces immediate results, but also instils the skills necessary for independent problem solving in the future.
Assessment - Assessment methods must take into account the zone of proximal development. What children can do on their own is their level of actual development and what they can do with help is their level of potential development. Two children might have the same level of actual development, but given the appropriate help from an adult, one might be able to solve many more problems than the other. Assessment methods must target both the level of actual development and the level of potential development.
The key to "stretching" the learner is to know what is in that person's ZPD—what comes next, for them. It is common in constructing skills check-lists to have columns for "cannot yet do", "can do with help", and "can do alone". The ZPD is about "can do with help", not as a permanent state, but as a stage towards being able to do something on your own.

8. Criticism
Some types of social interactions may actually hold development back.
There might be other reasons why people learn better in the presence of others (e.g. social facilitation)
Young children often take months/years to master certain types of skill even with appropriate social support – e.g., could a young child solve abstract problems? Suggests that cognition is constrained by ages and stages (Piaget’s idea)

9. References Extracted from and modified:
Grantham College Presentation