You obviously missed the whole point of the movie. It's a psychological drama. Not some space cowboy 'shoot-em-up' like Starwars or Starship Troopers. The practice battles - which you dismiss so lightly - are to show that whenever Ender wins - which he always does, even after they've given him an army of everyone else's rejects and some new recruits - they (Graff and co.) change the rules! They keep stacking the odds against him forcing him to come up with new ideas. (Perhaps you really needed to read the book to pick up on that fact because there are many more battles - then again, that might not have helped you understand why if the fact that they were mock battles - and not real blood and gore - bored you)
Ender is also a 'third' - ie. a third child born to a family in a time when families are limited to 2 offspring. Because of that he is despised by the other children which is the cause of the bullying at the start of the film (perhaps you also missed that point) The military let this be known to the other recruits to see how he reacts... the same way as when he ends up in the fight in the bathroom - Graff knows all about it but just lets it play out to see what happens - even though (in the book) Ender is only 11 and his antagonist is 14 and much bigger. The constant stacking of the odds against him eventually causes Ender to quit battle school - he has had enough of being screwed over by Graff - but Graff realises that he is still their best hope/candidate and uses Ender's sister to persuade him to go to battle school where he does further training.
At some stage the new training changes to reality - but Ender is not told that because they (Graff a & co.)don't want him to feel remorse or guilt over the killing of the enemy or, even worse, realise that when he loses ships in parts of a 'game', those ships are actually real and human soldiers are actually dying! (In the book, Bean is the first to figure that out but still keeps it secret from Ender!) That is one of the major points of the film - the concept of DECEPTION. The military have been deceiving him and setting him up all along to test him and still let him think it is all just a game right up until the end.
When Ender does find out that he has wiped out another race and sacrificed real soldiers as a part of his 'game' strategies he is devastated. That is the purpose of the final scenes - when he also realises that the 'aliens' (for want of a better word) had already realised his importance in the scheme of things and had tried to communicate with him through the 'game' on his desktop. (perhaps you didn't pick up on that fact)
Your comment that Maser Rackham sounds like a South African Maori is noted. Keep in mind that as the movie is set in well into the future and given the amount of South African's migrating to New Zealand it's not beyond belief. Also keep in mind that is does state that he is only 'part-maori' and no reference is made to the fact that he has actually been living in New Zealand. He could have been living in America or somewhere in Europe for that matter.