It is bigger than that. A key part of the book are the two times that you have the kid who is the "hero" of the book beat other kids to death with his bare hands. I've heard this is one reason that a studio wanted desperately to make the characters teen to late teenagers for the movie. They did not want to show the "hero kid" beating another kid to death in the shower. But those two scenes are vital to the movie because they form the basis of why Ender is chosen to lead the war against the buggers. They want someone who will fight with ruthless finality and kill the buggers once and for all but someone who is also sympathetic enough that his fellow commanders will follow him without hesitation.