Lev Vygotsky

Lev was a Russian psychologist 
who did alot of studying on 
the devolpement children.  His 
works were not discovered until 
after his death at the age of 37.

He developed the "Zone of Proximal
Development" which is the time period 
a child can learn with and without 
an adult present.  He also wrote a book
entitled "Thought and Language", this 
book refers to how language is related 
to thought.
http://en.wikipedia.org/wiki/Lev_Vygotsky