Books like Shadow of the Giant

Bean's past was a battle just to survive. He first appeared on the streets of Rotterdam, a tiny child with a mind leagues beyond anyone else. He knew he could not survive through strength; he used his tactical genius to gain acceptance into a children's gang, and then to help make that gang a template for success for all the others. He civilized them, and lived to grow older. Then he was discovered by the recruiters for the Battle School.