Still-1_John-Gallagher-Jr_Brie-LarsonShortTerm 12
John Gallagher, Jr. and Brie Larson shine in "Short Term 12," opening in limited release on August 23. Brett Pawlak/Cinedigm

Early on in “Short Term 12,” a young woman with a broken heart of gold asks her boyfriend, “Why are you so nice to me?” You may find yourself asking this question of the movie itself. Destin Daniel Cretton’s second feature, adapted from a 2009 Sundance award-winning short of the same name, is a stunning, generous film that leaves its audience with little to nitpick or argue about, save maybe this: If you don’t like this movie, I don't like you.

While there is not a shred of cynicism in its execution, to call “Short Term 12” a feel-good movie doesn’t feel quite right. It takes place in the titular group home for adolescents who have nowhere else to go; it's told through the eyes of Grace (Brie Larson), their lead daytime supervisor, whose own history of abuse and trauma has kept her trapped on an emotional hamster wheel. Her co-worker and boyfriend, Mason (John Gallagher Jr.), also from vaguely troubled beginnings, feels indebted to a transformative second chance that those he looks after may never get. Each fiercely kind and strong, Grace and Mason make a powerful, immensely likable pair. They’ve both been doing this work for a few years, and wear their responsibilities like a second skin.

But though they are intimately involved and deeply invested in the everyday lives of Short Term 12 residents, they have little control over what will ultimately happen to them. (For example, if someone goes “AWOL” and makes it past the building grounds, the supervisors can’t touch them -- all they can do is reason with them to return.) Nate (Rami Malek), a recent hire, trips over his good intentions in his first, shell-shocked hours; and gives us an early taste of the expertly portioned levity that keeps the story from collapsing under its weight. The tone of the movie is as upbeat as it can honestly be, with genuinely funny moments, but it would be impossible to guarantee a happy ending for all.

Whether our first introduction was “To Sir With Love” or “Lean on Me” or “Freedom Writers," by now we can all identify the deadly familiar narrative trope of the devoted teacher as savior to marginalized youth. “Short Term 12” is in this world, but not of it. The supervisors don’t have the time or the luxury to be inspirational. In place of motivational speeches and melodramatic epiphanies are daily room checks for drugs and weapons, and regular, high-alert crisis interventions. Their dictum is to keep their charges safe (and nothing more); and as some are given to self-harm and violent outbursts, every single day is a battle.

This is not to say that the residents of the home are hopelessly dangerous budding criminals. Perhaps following the example of their supervisors, some show a devastating capacity for kindness, and you don’t get the sense that they really want to give up on themselves, despite frequent displays of deep apathy and self-destruction. Marcus (Keith Standfield), who has been there longer than anyone, is nearing his 18th birthday and mandatory release; his crippling fear of being cast back out into a world that has never been kind to him is written all over his face and in his conflict with one of the younger boys. Still, he is responsible for one of the most heartbreakingly compassionate gestures in the film.

We can assume that terrible things have happened to anyone who is living at Short Term 12, but in most cases, we don’t see or hear much about the particulars. When we get hints at backstories -- as we do with Marcus, or Jayden (Kaitlin Dever), the 15-year-old “cutter” and the newest arrival -- they are revealed (and obscured) through their art. And it’s through Jayden that we learn more about Grace’s painful history, details that help to explain why, even in her admirable self-sacrificing, she can’t seem to get out of her own way.

Most anyone who stuck with the Showtime series “The United States of Tara” will recognize Larson, who played Toni Collette's openly, warmly rebellious daughter Kate, as a reason to have kept watching. I reckon Kate wasn't written as a show stealer; that Larson lit her up just enough to keep our eyes on her but not so much as to cast a shadow on the whole operation. In “Short Term 12,” Larson is free to shine, and shine she does, giving one of the best and most believable performances you will see this year.

Gallagher’s Mason is the kind of boyfriend every girl would dream of having, but probably couldn't unless she had a broken wing or two. An underdog with a soft spot for the underdog, Mason is the ultimate success story of at-risk youth, and he has never forgotten what the kindness and generosity of strangers can do for people like him. Unflappably good-humored, Mason does pretty much everything right; and the same can be said for Gallagher.

If there's a quibble to be found, it is in the climax of the third act, when there’s almost too much going on, and where a key conflict feels both predictable and forced. And some might find the camerawork to be a little bit too decidedly “low-budget indie.” But perhaps the talented team behind “Short Term 12” just didn’t realize what they had on their hands. In fact, the strongest and only fair criticism you can make about this movie is that it doesn't take itself seriously enough. As far as flaws go, it doesn't get much better than that.

"Short Term 12" opens in limited release on Aug. 23.