Inspirational urban high school sagas must have irresistible appeal to major-league actors. Maybe roles involving the compassionate educator who activates young lives and redeems lost souls serve as a reminder of their own turning point, or maybe they want to make a movie their own children can watch, or maybe they’re just suckers. There’s got to be some compelling reason, because the movies are so formulabound that there are never surprises — except when the star nabs the occasional Oscar.

Hilary Swank already has two, for playing tragic underdogs in “Boys Don’t Cry” and “Million Dollar Baby.” So, obviously, that can’t be her motivation for “Freedom Writers,” an extremely well-meaning drama that is so earnest it hurts. Set in Long Beach, Calif., in 1992, in the wake of the riots that followed the Rodney King verdict, the film is based on a true story. That story concerns plucky, indefatigable teacher Erin Gruwell (Ms. Swank), who found a way to get through to a tough, sullen classroom full of delinquent youngsters whose lives were swallowed up in street warfare between black, Asian, and Hispanic gangs — with a hapless white boy thrown in for good measure. They’ve all wound up at Woodrow Wilson High School as part of a voluntary integration program, and they’ve turned the formerly top-ranked school into a holding pen for budding felons.

The key to transforming children whom everyone else had written off was to make them see a world beyond their own strife, and to give them back ownership of their lives. The real-life Ms. Gruwell introduced her class to “The Diary of Anne Frank,” apparently buying the books with her own money when her administrators balked at her optimism, and got her students to keep daily journals. The results were so dramatic that the group christened itself the Freedom Writers — a play on the civil rights activists known as the Freedom Riders — and eventually published their stories. A high percentage of the students graduated and went on to college.

Director Richard LaGravenese (“Living Out Loud”) sticks with the program, contrasting the Pollyanna-like enthusiasm of Ms. Swank with the anger and contempt of her students to often comic (and predictable) effect. As the kids’ individual stories develop, accompanied by narration from their journals, the movie threatens to acquire some depth. There are genuinely good, moving performances by a cast of young unknowns, who follow a narrative arc that borrows heavily from “Boyz n the Hood.”

Much of the rest feels contrived and underwritten. Patrick Dempsey (“Grey’s Anatomy”) plays a self-pitying husband who whines because his wife is spending too much time with her charges and working extra jobs to finance field trips. He’s no Dr. McDreamy. Instead, he acts like one of those selfish lugs that turn up on “The Dr. Phil Show.” This may be some kind of point, but the character seems shallow. Likewise, the condescending teachers and principal at Woodrow Wilson, imagined as sniffy, two-dimensional stock characters who wandered in from a comedy like “Rock’n’Roll High School.”

Ms. Swank sails through on a boundless supply of good cheer, working her gawky charms as she awkwardly embraces hip-hop lingo and strives to meet the children on their own level, dispensing plenty of hugs and tears. The hanky factor is high, and while there is a sturdy moral message about racial tolerance to bolster the mood swings, it never lifts the film above its genre. Strangely, too, it’s almost a period piece. Fifteen years ago, teenagers had yet to be empowered with ubiquitous cellular phones or to turn into texting fiends who dispense with legitimate English for a flurry of abbreviations. As such, “Freedom Writers” is almost quaint.