Card, Orson Scott.
In order to develop a secure defense against a hostile alien race's next attack, government agencies breed child geniuses and train them as soldiers. A brilliant young boy, Andrew Ender Wiggin lives with his kind but distant parents, his sadistic brother Peter, and the person he loves more than anyone else, his sister Valentine. Peter and Valentine were candidates for the soldier-training program but didn't make the cut--young Ender is the Wiggin drafted to the orbiting Battle School for rigorous military training.
Publisher: Orbit, Paperback, 2011.