Warning: Wikipedia contains spoilers.
Card went back and expanded the short story into a novel after realizing that he wanted to use Ender as a main character in another novel, Speaker for the Dead. The series subsequently gained two further books (Xenocide and Children of the Mind) and has spawned a companion series of novels, the Shadow series (Ender's Shadow - a parallel novel to Ender's Game, telling some of the same events from the perspective of Bean, a mostly peripheral character in Ender's Game - and its sequels, Shadow of the Hegemon and Shadow Puppets to date). The original short story is merely a snapshot of Ender's experiences in Battle School; the full length novel is a deeper and more complex work dealing with Ender's life before, during and after Battle School, and the consequences of his final battle with the alien 'Buggers'.
Some military colleges have used Ender's Game as a textbook on leadership.
Ender's Game was the winner of the Hugo Award for best novel in 1986 and the Nebula Award for best novel in 1985, the two most prestigious awards in science fiction. It was reprinted in a slightly revised edition in 1991.