Parents just don't understand. That's the message of Lee Hirsch's powerful documentary "Bully." The parents of kids who behave thuggishly to their classmates shrug off child-on-child abuse as "kids just being kids." The families of children on the receiving end of nonstop mistreatment don't comprehend their suffering. The parents of 17-year-old Tyler Long, allegedly the victim of longtime harassment by his classmates, didn't realize how he felt until he hanged himself in his bedroom closet.

David and Tina Long have been battling school bullying in Georgia since their son's 2009 suicide. Their story is one of five told in the film, which Hirsch filmed over the course of a year with no lights, no sound person and only a small video camera. While his film is limited in scope (all his subjects live in fairly rural settings), it reflects a sadly prevalent state of affairs.

From the Longs, the film moves to Alex Libby and his family in Sioux City, Iowa. "I feel kind of nervous about going to school," says Alex, whose classmates ostracize him. "I like learning, but I have trouble making friends." He enters seventh grade fearful it will be another chapter in a continuing story of humiliation. "They punch me, strangle me, take things from me, sit on me. Sometimes they push me so hard it makes me want to be the bully," he says. Alex's mom brings the problem to the school principal, who -- apparently more concerned with saving face than addressing the problem -- shrugs off her concerns.

But Hirsch's film captures the perspective of Alex and other victims: physical abuse, insults and threats, school bus rides that resemble mob scenes from "Lord of the Flies." It's painful viewing, but necessary. Catharsis often involves going to dark places.

Although Alex is encouraged by his dad to fight back, he seems temperamentally inclined to tough it out in hopes the abuse will flame out. On occasion, bullied kids do lash out at their tormentors. When her school bus rides became an ordeal of ridicule, Ja'Meya Jackson, 14, brandished her mother's handgun. The event was captured by the onboard camera, and Ja'Meya was arrested and placed in a detention center, facing 45 felony counts. Hirsch interviews a local law-enforcement official who says, "unless someone was hitting this young lady in the head and being physically brutal to her, there's nothing to me that justifies her taking her gun on that bus, I don't care what it is." At Ja'Meya's hearing, a judge sensitive to the cause and effect of aggression dismisses the charges; another might have saddled her with a juvenile record.

Not every story is so dire. Kelby, a lesbian teen in Oklahoma, seems destined for happier times after high school. She recalls her teacher taking attendance by "boys," "girls" and after a pause, "Kelby." She tells of being roughed up by boys and even deliberately struck by a minivan full of classmates, but laughs off the incidents with robust good humor. "If I leave, they win," she says. A star athlete with a supportive family, friends and a generous supply of self-confidence, she's positive that a better life awaits her after high school.

"Bully" features two families who lost children because of bullying-related suicides. They channeled their grief into direct action, convening community discussions and setting up social-media forums to publicize the problem and explore solutions. "I will go to my grave until a difference is made," says Tyler Long's distraught dad, and you know he means it. For the sake of the other kids in the film, you pray he'll succeed. "Bully" is less a checklist plan for eliminating abusive behavior than an emotionally powerful wake-up call for a society too long in denial.