Lev Vygotsky was born on November 17, 1986 and unfortunately died on June 11, 1934. Vygotsky is known for his zone of proximal development, which is basically what a child can do on their own and what they can still achieve with assistance. There's an outer layer which is known as the task that is too difficult for the child, an inner layer which is too easy for the child, and then there's the middle which is the zone of proximal development which is just right for the child. A technique Vygotsky used is scaffolding, which is simply praising a child or correcting a child in a nicely structured manner.
Here's an example of ZPD http://m.youtube.com/watch?v=iaRb01SEWmY