In a future in which alien arms attack the planet, mankind must prepare for war. Those children who are by nature apt to become officers are educated separate from mankind. They are taught to play at war & the science required for modern war. They are not expected to invent scientific things, only to know how to use the things they have. Within these limits, they have to invent things regarding war.
Why should children be preferred to adults? When Ender is taught to shoot, he receives praise for not having any bad habits. The children are surprisingly quick to forget their parents, because they are busy with each other. It is their willingness to do the unthinkable, at least if they do not know what they are doing. There appear to be two kinds of ignorance: Taking orders & not distinguishing speech from deed.
The children are taken off-planet to learn space warfare. But they do not fight so learning 3-d simulators might suffice. What they are learning is to lose their human home. This is necessary to save the human home. They will all sacrifice. Being children, they do not know. But all the fleets sent out – those men do know.
Our hero, Ender, is a spontaneous Clausewitz. Without gravity, we must think the enemy is down: Attack his center of gravity. War is about making something into nothing. This is an attack on creation. When he fulfils his warlike ambitions, Ender has a crisis of identity. He is the monster he hated in his cruel brother. His tender sister cannot protect him from war, as she could not protect him from his brother. He has to protect her. Is he willing to sacrifice his humanity?
Ender has two teachers. Graff is careful to push Ender always to feel alone & in danger. This weakness, this neediness is essential to give form to his martial habits. Graff is the man who gives form to the necessities of war. He trains an officer corps which can execute orders. Ender can never be allowed pride because defense requires knowledge. Rackham teaches him to learn from his enemies therefore. To see the alien as if human; to see mankind as an alien does.
Ender fears that in understanding things, in feeling as others do, he comes to love them, but then he has to destroy them anyway. This contradiction is what caused his crisis. His masters seem to agree. Nobody is killed in the school of war. Ender never suggests he might start killing people like the aliens do. Nor that his newfound art of war might turn on his masters. His masters seem to make an education of this contradiction.
The only movie made out of one of the more interesting & successful SF stories. Young men should see it.