The key to Jack Black’s tour de force performance in Richard Linklater’s “School of Rock” is less his sense of music and more his flair for drama.  When the children in his class ask him to sing the song he’s written, Black launches into a mesmerizing enactment of a rock opera that sounds a lot like something the guys in Spinal Tap would have have lapped up with a spoon. It isn’t even that he imagines his song as a video (“MTV ruined everything” he whinges) but as part of some Arthurian slacker drama. Loving rock and roll is his way of escaping into another world, as it is for most people, except his world is scored by Andrew Lloyd Webber with lyrics by Robert Plant.

The gallery of hammy dramatic faces he makes onstage are priceless, but they’re even funnier in the more banal situations in which he finds himself.  Black has a matchless talent for mock-epic, making his Dewey Finn compulsively watchable. Much of the music that the movie holds forth as “pure” rock and roll is also pure drivel. Given the knockoff Rolling Stone logo on the movie posters, it’s not surprising that Dewey’s tastes are frighteningly reactionary. Even more frightening is the way bands as diverse as the Sex Pistols and Pink Floyd are stuck under the same “rock” umbrella; I wonder what sort of reaction Black would have gotten from Johnny Rotten if he’d tried that in the late Seventies.

By failing to differentiate between the Pistols and Pink Floyd, or between The Ramones and Led Zeppelin, the movie loses the purity which it wants to uphold. It’s not enough to claim that he’s channeling the “spirit” of rock and roll, because that comes under a myriad guises. Instead, Linklater lets three decades of rock and roll grade together into a shapeless lump of bland noise.

This is nitpicking. Any objections that arise are rendered irrelevant by the sheer madness of Black’s crusading loser. So complete is Dewey’s love of rock and roll that he begins to cross over into Don Quixote territory, charged with a delusion so complete you can’t help but wonder if you’re not a fiction alive in his reality.  He glows with such infectious passion that it’s easily possible to like the character without liking the music.

Linklater gets out of Black’s way, instead focusing on bringing out charming performances from the children. The kids are combed and coddled prep-school types, especially alpha-female Summer (the adorable Miranda Cosgrove), and unlike other specimens of this genre there isn’t a lot of time wasted discovering what special little snowflakes they are. The kids are believable musicians, mostly, except when they appear for the last Battle of the Bands number, which resembled the climax of “Revenge Of The Nerds” a little too closely.

The interaction between Dewey and the kids is sweet, genuine, and funny, probably because he’s no more mature than they are. Until the Tenacious D movie hits the screen, “School of Rock” will serve as the defining testament to Jack Black’s greatness, and a worthy testament it is. Although Mike White (“Orange County”) turned in another script that’s twelve shades of vanilla, and Linklater is happy serving up a likable formula film, Black singlehandedly carries the day with a performance that’s ablaze with a quality seen only in the greatest film performances: real passion. More than a few eager young recruits will leave the multiplex clamoring to start bands of their own. Let’s hope he does something about his taste in music.