Ender's Game by Orson Scott Card
Young Ender Wiggin thinks he is playing war games at the Battle School, high in orbit, but he is engaged in something far more desperate. Ender may be the military genius Earth desperately needs in a war against an alien enemy seeking to destroy all human life. The only way to find out is to throw Ender into ever-harsher training, to chip away and find the diamond inside, or destroy him utterly.
Lexile Measure: 780L
Literature, Science Fiction, Fantasy. Author: Orson Scott Card. Paperback edition, 324 pages, 6 x 4 inches.