Boot Camp, by Todd Strasser
Although the topic and setting might appeal to at-risk kids, the main character represents only one fraction of that audience. He's prodigiously gifted, extraordinarily wealthy, and one half of an anomalous relationship. He's as big a misfit (largely due to his honesty) at the boot camp as he is elsewhere. In spite of (or because of) his advantages, Garrett is an extremely sympathetic character, and that makes the story work.
The events of the book are unsettling and believably rendered right up to the end.