Dan, an idealistic young white history teacher, faces a daunting classroom full of bored African-American kids in Brooklyn: Can he and his offbeat approach inspire -- perhaps redeem -- them in general? A sullen girl named Drey in particular?

Ryan Gosling, right, plays Dan Dunne, an idealistic inner-city junior high school teacher, who harbors a secret drug addiction while trying to inspire his students. Click photo for larger image. 'Half Nelson' Starring: Ryan Gosling, Shareeka Epps, Anthony Mackie, Tina Holmes. Director: Ryan Fleck. Rating: R for pervasive drug content, language and some sexuality. Web site: www.halfnelsonthefilm.com

You instantly recognize the formula and instinctively think yes. But you are instantly and instinctively wrong about director Ryan Fleck's "Half Nelson," a desperately contemporary tale of horrendous drug addiction in our schools.

That's because of this excellent movie's narrative switcheroo: The crack habit at issue in the junior high at hand belongs not to Drey (Shareeka Epps) but to Dan (Ryan Gosling), her troubled teacher, basketball mentor and problematic friend.

She discovers his secret soon enough and, we come to find out, knows more about the crack business than he does: Drey's mother is a good, hard-working cop. But her mom's ex-boyfriend is the dealer (Anthony Mackie) who not only supplies Dan with his "candy" but is looking to enlist Drey in the business.

Rather than the official curriculum, Dan teaches a Marxist dialectical materialism of opposing historical forces -- for which he gets in trouble, of course. He wants to rescue his kids from the oppression of society, while his star kid wants to rescue him from dope. Both of them are largely doomed to fail. Dan's drug use is a symptom of his misfit's inability to cope with life and his need to numb reality.

"Half Nelson" is a bad title, referring to the hold of drugs on the hero. But Gosling's performance in it -- as in "The United States of Leland" and "The Notebook" -- is superbly nuanced and low-key, reminiscent of the early De Niro. Young Epps, with her beautifully enigmatic face and naturalistic delivery, is a true discovery, a perfect match to Gosling in strength and intelligence, pain and pathos.

"We're always changing," says Dan. "Some changes you can control, some you can't." The film's ambiguous ending leaves the conclusion of hope or despair up to us.

Opening today at the Squirrel Hill Theater.