Nearly everything about "School of Rock" counts as a pleasant surprise, from its unexpectedly robust entertainment value to its unexpected suitability as family entertainment (despite a PG-13 rating for rude humor and some very subtle drug references).

Jack Black displays the explosive and infectious energy so notably lacking in his prior starring role (in the disappointing "Shallow Hal") and deepens and fills out the doofus, stoner, supporting parts in the slacker comedies ("High Fidelity," "Saving Silverman," "Orange County") that made him famous. This time he plays a music mad rebel who's bounced from his rock group and threatened with eviction for non-payment of rent by his substitute teacher roommate (Mike White, who also wrote the screen play).

In order to bring home some emergency cash, he impersonates that roomie to take a job teaching fifth grade at a prestigious, fiercely competitive private school, hoping to avoid detection by the bespectacled, martinet principal (Joan Cusack). Unable to pass the classroom time in teaching any conventional subject, he decides to mold his young and uptight charges into a face-meltin', gut-bustin' rock n' roll juggernaut that can compete in a local battle of the bands.

The kids in his class emerge as distinct, vivid, enormously likeable characters thanks to superior performances by a cast of pre-teen unkowns (Joey Gaydos Jr., Maryam Hassan, Kevin Clark, Rebecca Brown, Robert Tsai, among them) and the supremely skillful direction by Richard Linklater ("Dazed and Confused," "Before Sunrise"). The heart of the movie shows Black teaching his kids the essence of rock 'n roll (including its anti-establishment, angry attitude) and unlike lesser films (does anyone remember the pallid "The Fighting Temptations"?) you can actually watch these kids mastering their musical chops. The plot provides both consistent laughs and frequent surprises (including an ingenious conclusion that overthrows every cliché involving climactic competitions).

Watching the movie with my eleven-year-old son (the same age as most of the kids in the movie), I worried that the underlying message would encourage disrespect for classroom discipline and competitive academics--- pointing my chilld (and yours) in exactly the wrong direction. Amazingly enough, screenwriter White (who also wrote the acclaimed Jennifer Anniston vehicle "The Good Girl") and director Linklater show rock n' roll as a liberating supplement and occasional release, rather than a replacement, for the serious school work that the parents and administrators emphasize in the movie. The kids celebrated in the film display intelligence, creativity and underlying decency, rather than nihilism or an instinct for self-destruction. It may seem anomalous to suggest that the manic, anarchic Jack Black comes across as a wholesome influence on the young people in the movie (and in the audience), but he somehow manages that seemingly impossible task.