Just watched an amazing documentary on childhood brain development. They studied how the formative years of a child from 3 months to 7 years is absolutely crucial to their brain development. Children that received special schooling were able to learn language faster, speak more coherently, and able to perform much better at school and later in getting good jobs.
There was also a very sad story about an abused child who was kept locked up by her crazy parents until their crime was found out when she was 8 or 9 years old. Because they did not speak to her, treating her worse than an animal, she initially had the mental capacity of a baby. A childhood psychologist tried to teach her and found her very intelligent. However, perhaps because her horrendous neglect - she was unable to recover. Placed into several foster homes, including one which sexually abused her, she is now placed into a "home".