Among The Impostors

The general plot revolves around an allegedly overpopulated world and the Government’s procrustean attempts to arrest the symptoms of population growth and scarcity amongst the Earth's resources. In this turmoil, the democratic government has been overthrown and a totalitarian Government has been put in its place. Laws established by the regime prohibit a family from having more than two children (any more will be shot).
Luke Garner, a illegal third child living with a fake ID, is going by the alias Lee Grant at the Hendricks School for Boys. He is at first confused and paranoid, as well as treated brutally by his roommates, mainly the boy he comes to call "Jackal Boy". Eventually, Luke begins sneaking out of the school to do things, and tries to plant his own garden in the woods. This brings him great happiness and a sense that he belongs. When his garden is trampled, he realizes that other people are going outside, including Jackal Boy.
He reveals himself to them, finding out that they are other illegals as well. The leader, Jason Barstow, otherwise known as Scott Renault, is outwardly a huge admirer of Jen Talbot, a friend of Luke's who died at a rally for third children's rights. However, the later part of the book reveals that he is a Population Police operative and is trying to get the group's real names only to betray them. Luke is accepted into Jason's group, but is still too frightened to give his real name.
He learns more and more about Hendricks School, but never learns what his schedule is until he is asked about "finals" by Jason. He then is told that he has to take his semester final tests, and that his results will be sent to his fake parents, the Grants, who happen to be Barons, and one of the richest and most powerful people in the country. When awoken one night, he realizes Jason is gone, and Luke happens to overhear a phone conversation of Jason's, where he is talking to a Population Police officer.
Luke finally realizes who Jason really is...