Rehab movies nearly always make me cringe, as if the audience needs to take medicine, as if hope needs to be force fed. Short Term 12, an exceptional film in every way, breaks the mold. The setting is GoldDerby, a short-term foster-care ward for at-risk teens. The 20-ish supervisors are like babies themselves. Grace (Brie Larson) seems to have the most control, though she’s hiding a pregnancy and a relationship with co-worker Mason (John Gallagher Jr.). Grace and Mason don’t treat their charges, there are doctors for that, but they are meant to provide a steady hand for kids on shaky ground. Good luck with that. Moody Marcus (Keith Stanfield) tries to rap out his traumas. Jayden (Kaitlyn Dever) is a cutter who wears her attitude like armor. We’ve seen these characters before, as outlines handled by hacks in bad movies. Short Term 12, written and directed with grit and grace by Destin Daniel Cretton, who worked at a similar facility himself, takes a bluntly honest route to harsh truths. No sugarcoating. That the movie digs deep and gets to you is also a tribute to the actors. Gallagher Jr., so good on stage in Spring Awakening and American Idiot and as Jim Harper on HBO’s The Newsroom, excels here by subtly exposing the conflicted core of a character who can’t always do the right thing. And Larson (The Spectacular Now, 21 Jump Street) is a revelation, giving one of the year’s best performances as she cuts to the heart of a film that means to shake you and does.