Ender's Shadow by Orson Scott Card

Ender's Shadow (The Shadow Series) - This is the story of Bean, the boy who became Ender Wiggin's right hand man in Ender's Game.  As an orphan on the streets of Rotterdam, Bean, was the smallest of the small, but more intelligent than any other.  Knowing he could not survive through strength, Bean learned through observation and insinuated himself into a street gang by giving strategic advice to the leaders.  This brought him to the attention of those responsible for recruiting children for Battle School.  In Battle School, Bean again learned by observation and infiltrating the teachers' systems to learn everything he could about the other children and why they were being groomed for battle.