So, the problem (well, the relevant problem) with the movie is that it's not as subtle as the book is. You know how, in the movie, he becomes a leader in his Launchie group in about three days? In the book, it's longer.

Then he's in Bonzo's army, and he learns how to become a soldier (yes, Petra helps him, though it's not quite as huge a deal).

When he becomes a commander, he has to figure out tactics, learn how to command, there's a subplot where he does to Bean what Graff did to him, etc.

This is all interspersed with a sideplot involving Ender's siblings.

The two plots come together when Ender's down at the lake, and you get a lot of good character development instead of a few lines spoonfed to the audience. (Much of that dialogue IS, in fact, in the book, but it's spaced out, given more context, given some introspection, etc.)

Command School? Is supposed to be this long, grueling, isolated experience where Ender is this close to the breaking point from exhaustion.

I think the problem you had was that the violent and traumatic stuff comes relatively quickly. Instead of 50-100 pages of development and context between violent events, you get 15-20 minutes.

Seriously, go read the book. It will give you context for a LOT of the events of the movie.