My biology teacher's sister adopted two Russian brothers when they were about six and eight, I think. They had been malnourished and had spent much of their lives effectively alone. They were unholy terrors for a long time. He said they're doing better--physical work for the older one seems to help a lot.

A friend of mine was adopted, as was her (non-biological) brother, both as infants. They've both got some issues, but the brother's were worse. He'd get into a lot of trouble at school, and ended up threatening his sister. Long story short, she got sent to a school in Virginia (I don't know the whole story), they got some kind of help for the boy. My friend wound up dropping out of college and is now working at a bakery.