'Have you heard about those mothers that lift one-ton trucks off their babies? They're nothing compared to me!"

That's Maggie Gyllenhaal talking, bouncy and defiant as Jamie Fitzpatrick, a struggling single mom determined to do something about her daughter's broken school. John Adams Elementary stands in a decrepit corner of Pittsburgh, and its worn-out faculty turns out students who can barely read.

Worse, in Won't Back Down, Malia Fitzpatrick (Emily Alyn Lind) has dyslexia. She is taunted by her fellow third graders, while her teacher sits at her desk, trolling the Internet for shoes. Jamie, who works as a bartender by night and receptionist by day, tries to get Malia transferred to another class, but the principal won't budge.

A kind of Norma Rae for the Paul Ryan set, Won't Back Down ("inspired by actual events") follows Jamie as she channels her frustrations, and her promise to give her daughter a quality education, to lead a rebellion against the Adams administration and the school district itself. Citing "parent trigger" legislation that allows for the takeover of a failing school, the tattooed barkeep who can barely rouse herself from the couch in the film's opening credits becomes a sedulous petition driver, taking a bullhorn in hand - and not taking no for an answer.

Directed and cowritten by Daniel Barnz (Beastly, Phoebe in Wonderland), Won't Back Down incorporates many of the grim facts about the U.S. education system documented in Davis Guggenheim's Waiting for "Superman," and applies a kind of David vs. Goliath Hollywood overlay.

But while the obstacles (daunting) and the outcome (uplifting) are predictable, Won't Back Down benefits hugely from its cast: Gyllenhaal is relentless (the actress and her character), and Viola Davis, who plays Nona Alberts, an Adams teacher who, warily at first, becomes Jamie's ally, brings grace and gravitas to her role. Davis is amazing - all she need do is take to a flight of stairs and she somehow manages to convey a complex whorl of dreams and woes.

Oscar Isaac is another Adams staffer Jamie tries to get on her side. He's a great teacher (he plucks a ukulele! he gets his kids to line dance!), and hey, he's awfully cute. But Isaac's Michael grew up in a union household, and Jamie's fight to take over Adams means he would lose his union affiliation and all the hard-won benefits and job security that come with it. And so, in Won't Back Down, the enemy isn't just a top-heavy, intransigent school bureaucracy, it's the teachers' union itself. Holly Hunter and Ned Eisenberg play the union leaders, circling their wagons and plotting smear campaigns against Jamie and Nona.

Barnz tries, at least a bit, to acknowledge the heroic and historic legacy of the union movement and its rightful place in the contemporary labor landscape. But much of the blame for the sorry state of Adams Elementary, and the school system at large, is placed at the union's feet. That image of Sally Field hoisting a sign that reads UNION in Norma Rae? In Won't Back Down, Gyllenhaal might just as well have a placard that reads UNION - NO!