Dan Gemeinhart: Scar Island

Jonathan Grisby is the newest arrival at the Slabhenge Reformatory School for Troubled Boys – an ancient, crumbling fortress of gray stone rising up from the ocean. It is dark, damp, and dismal. And it is just the place Jonathan figures he deserves.
Because Jonathan has done something terrible. And he's willing to accept whatever punishment he has coming.
Just as he's getting used to his new situation, however, a freak accident leaves the troubled boys of Slabhenge without any adult supervision. Suddenly the kids are free, with an entire island to themselves. But freedom brings unexpected danger. And if Jonathan can't come to terms with the sins of his past and lead his new friends to safety... then every boy on the island is doomed.
Dan Gemeinhart's most gripping novel yet, this is a tale of misfits and outcasts at odds and in peril, and a redemption story that shines a light on dark truths to reveal that the strongest prisons of all are the ones we build for ourselves.