"Short Term 12" is a small wonder, a film of exceptional naturalness and empathy that takes material about troubled teenagers and young adults that could have been generic and turns it into something moving and intimate.

"Short Term 12," named for the foster care group home for children younger than 18, where it's set, is anchored by the generous and persuasive acting of Brie Larson as a staff supervisor, a performance that won the actress award at the prestigious Locarno Film Festival. Much to the credit of writer-director Destin Daniel Cretton, whose two years of post-college work in a similar facility is key to the film's verisimilitude, "Short Term 12" also took the audience award at the Los Angeles Film Festival and at South by Southwest, where it received the narrative feature prize as well. This is an accessible film that honestly earns every bit of its emotional effect.

Critical to "Short Term 12's" success is its gift for believability, for putting on screen people who are unmistakable individuals. In a larger sense, this is a film about the riskiness involved in both caring for another human being and having someone else care for you.

Helping this process is writer-director Cretton's natural storytelling gifts. Though "Short Term 12" holds us at once because of the immediacy of its characters, the film's actual plot is revealed only gradually, shrewdly doled out in a series of small surprises. Things may be hidden, but we never feel in the dark because the film in effect seduces us into its protagonists' lives before telling us all about them.

"Short Term 12" opens with 20-something staffer Mason (an excellent John Gallagher Jr. of "The Newsroom") telling new hire Nate (Rami Malek) a long story about something that happened to him on the job, a scene that showcases Mason's easygoing nature and genuine empathy.

It's a quality Mason has to call on before he can even finish the story, as young Sammy (Alex Calloway) makes a hell-for-leather break: If Sammy can get outside the property, the staff isn't allowed to touch him.

Helping Mason run Sammy down is Grace (Larson), the line staff supervisor. Also in her 20s, she is the even-handed calm at the center of the perennial storm that circles around troubled kids. With their different strengths, she and Mason make an effective team.

Though the kids don't know it, Grace and Mason are also a caring, in-love couple in their private life, sharing an apartment together in secret. But nothing is easy in "Short Term 12," and we find out almost immediately that Grace has to deal with personal news that strikes her as less than joyous.

As strong as Larson and Gallagher are as Grace and Mason, one key to "Short Term 12's" success is how well thought out and well cast (by Kerry Barden, Paul Schnee and Rich Delia) the kids under their care are. Kids like the traumatized runner Sammy or the cocky Luis (Kevin Hernandez), kids whom everyone has forgotten or tried to forget. Because they know this, there is an air of wariness and danger to them, the ever-present possibility that they will do damage to themselves or others. Even the toughest-seeming are vulnerable, hiding scars from a childhood that might as well never have happened.

Nearing 18 and mandatory release, Marcus (Keith Stanfield) is the oldest and one of the film's focuses. Intense and quick to anger, he expresses his feelings only in furious rap lyrics lamenting "a life not knowing what a normal life's like."

The arrival of 15-year-old Jayden (a poised Kaitlyn Dever) changes the dynamic of the house. Coming from a well-to-do background, she tells her new housemates she won't be talking to them because she doesn't want to waste her time on short-term relationships.

Smart, bored, entitled though she is, Jayden touches something in Grace. Though no one knows better than Grace the support staff mantra that "you're not their family, you're not their therapist, you're there to create a safe environment," she cannot help but want to get involved.

Given equal weight with what happens between the staff and these kids is what happens between Grace and Mason, a nuanced relationship that gets increasingly complex as different, unexpected aspects of their backgrounds get revealed. So many difficulties need to be surmounted in "Short Term 12" that any respite that can be achieved feels so much sweeter for the struggle that went into it. Sharing pain is the most difficult thing, but it also turns out to be the only thing that makes life bearable.

kturan@tribune.com

No MPAA rating

Running time: 1:36

Opens: Friday