"Short Term 12," which mostly takes place inside a foster-care facility, has a special atmosphere. Its mood is melancholic and thoughtful, very much focused on the quiet interactions and movements within people and on the culture of the place as a whole. The teenagers who live there are supervised by workers in their early and mid-20s. And more than the young leading the young, there is a quality of the wounded leading the freshly wounded.

‘SHORT TERM 12’ Rated: R Opens today at Kahala 8

This atmosphere — partly sad, and yet energetic, because everyone there is so young — is half of what’s memorable about "Short Term 12." This place, which most of us have never thought of, becomes specific and real, such that we can know we would not wish to live there and yet can see that it’s a home. The residents are like the kids. The young people on the staff, male and female, are like mothers, and the unseen authorities — the people who work in the offices making decisions — are like remote, authoritarian fathers, objects of respect and legitimate fear.

The other half of what makes "Short Term 12" memorable is Brie Larson as Grace, one of the workers. She makes us believe that she really has the gift for this — of caring, of authority, of knowing when to discipline and when to let up. Grace has a wisdom and gravity beyond her years, which means that she has a history. That history, gradually revealed, becomes essential to the movie.

The opening scene, seemingly casual, seemingly tossed off, sets up the story effortlessly. The attendants are taking a break, and Mason (John Gallagher Jr.) is regaling his colleagues with an anecdote at his own expense. Through it, we come to understand the rules of this facility. Basically, the attendants, if they catch a kid trying to escape, can subdue him and bring him back. But once a resident clears the fence, the attendants have no authority. They cannot lay a finger on anyone beyond the gate.

Much of "Short Term 12" is like that opening. The illusion is that you’re just seeing life unfold in this odd place, where deep need barely covers surface levity. But director Destin Creton, a Maui native, is following a tight structure. His film has an intricate design, and every part of it is leading to one direction — toward putting pressure, awful pressure, on his heroine.

Specifically, the movie takes Grace, the most levelheaded and competent of individuals, and gives her three profound sources of acute, inescapable stress: her relationship with Mason, her longtime boyfriend; her relationship with her father, which has been nothing but a source of horrific pain and misery; and the case of one of the residents, a teenage girl (Kaitlyn Dever), in whom she sees her younger self.

Among the wonders of Larson’s performance is in how she shows the near unraveling of this person. She is borderline unhinged in dealing with a psychiatrist who releases a girl back into the custody of her abusive father.

As Grace gets more desperate, Larson is always convincing, her thoughts always legible. Any director who sees "Short Term 12" will want to cast Larson in something. This movie puts her on the map.

But don’t forget John Gallagher Jr., as her remarkably sweet boyfriend, through whose eyes we see Grace. He’s the other half of her best scenes, and he makes Larson’s work possible.