Jack Black ain't got nothin' on Paul Green, a thirty-something force of nature who runs the Philly-based Paul Green School of Rock Music, an after-school program for future head bangers aged nine through 17. This joyous and riotously entertaining documentary works on several levels: as a portrait of a dedicated, if highly unorthodox, teacher; as a character study featuring several of his students; and as a "let's put on a show" feature in which Green whips his top kids into shape so they can appear at a German festival dedicated to the difficult, idiosyncratic music of the late Frank Zappa.

Green is no saint. A former rock musician, he's foul-mouthed, prone to temper tantrums, and can be downright cruel to his charges. But his love of the music, teaching, and his kids comes through no matter what, and despite the abuse he lays on them, it's obvious they'd go through fire to be by his side.

Like Will, a suicidal artist and admittedly mediocre musician, who admits that if he hadn't found Rock School, "I'd probably be dead." Green picks on him unmercifully at times, but it's a loving sort of needling, and you can tell from Will's response that he adores the attention.

Then there's Madi, a practicing Quaker with a booming voice and a mild, folky demeanor, who butts heads all the time with Green over her choice of material. Rock School features several full-blown screaming matches between the two, but Madi admits this creative tension has only made her a better musician.

Rounding out the cast of characters are Asa and Tucker, nine-year-old twins who want nothing more than to become heavy-metal gods, and 12-year-old C.J., a guitar prodigy who plays better than most adults.

Director Don Argott's film is composed of a series of impressionistic scenes, showing Green in all his glory as he cajoles and jokes with his charges and, admittedly, sometimes plays a bit too much to the camera (the retiring type he ain't). Tying the film together are two concert sequences, one a Black Sabbath tribute featuring Asa and Tucker as lead singers (during rehearsal Green, in order to get his 10-year-old drummer in the right mood, asks him, "Do you love Satan?"), the other the Zappanale, which comes off as a triumph for the kids-they absolutely slay the crowd of Euro hippies.

The great thing about Rock School is that it's a reminder of every dedicated teacher who has turned a kid's life around. Paul Green may be a little too offbeat, a little too much of the wild man for some parents, but there is no doubt he has made a difference to his students. That alone makes Rock School required viewing.