Since the kids on the bus were used to treating Alex with impunity and because Hirsch shot with a small Canon 5D Mark II, no one held back from hitting and cursing Alex just because a camera was present, which is where the footage that gave “Bully” its R-rating comes from.

Hirsch clearly developed a strong rapport with Alex, a bright, aware kid with an awkward manner who seems to confide in the filmmaker more than in his own parents. Alex is desperate for friends, and he doesn’t want to make waves, so he spends quite a bit of time trying to downplay the extent of his bullying, until Hirsch takes the unusual step of showing adults some of the footage he has shot.

For a variety of reasons, the two other teens depicted get less—and less effective—screen time than Alex. Though we hear from Kelby Johnson, a 16-year-old from Tuttle, Okla., who was ostracized when she came out as a lesbian, we do not see her being taunted. And young Ja’Meya Jackson of Yazoo County, Mississippi, who took her mother’s handgun to her school bus to stop chronic bullying, is in so much trouble that we hardly hear from her at all.

“Bully” is not comprehensive—the more modern torments of cyber bullying are not much dealt with—and it can feel haphazard as it jumps back and forth between its subjects.

Still, the film’s cumulative force is considerable, and, more than that, it shows the efficacy of a recent “I Stand for the Silent” campaign that encourages all kids to speak up when they see bullying taking place. Maybe, this film suggests, getting power to the powerless is not as impossible as it sounds.

Copyright (c) 2012, the Los Angeles Times. Visit the Los Angeles Times online at www.latimes.com. Distributed by MCT Information Services.