Light Years

The story begins on a mining planet where the unfiltered air will kill you after a few minutes. The wealthy live comfortable, but miner deaths are a frequent occurrence. A black market runner discovers that his older brother dies right before he was to go to fleet school off planet. The boy ends up taking his identity.

The civilization is at war with other groups. Things are so desperate that they are willing to take in people from "Edge" worlds into the military. This sets up your typical youth boarding school scenario. There are the rich that oppress the poor. The fashionable meet the functional and plenty of romances of various gender relationships break out along with requisite conflicts.

There are also plenty of nefarious activities. The "identity thief" bets against himself and uses the money to pay somebody to swap out his medical records so he won't get caught. One girl is a spy for the enemy race. The biggest scorn is laid on the boy who is a bigot towards the lower class people. 

There are the typical training and social dramas, then a real world invasion at the end. We also learn a bit about the enemy and that the conflict is not quite so black and white. There are plenty of open threads left for a sequel.