To the recent spate of documentaries about the triumphs and tribulations of youngsters and inspiring teachers you can now add “Rock School,” an energetic but ragged overview of the Paul Green School of Rock Music in Philadelphia. Of the many students who fill the halls and practice rooms of the charmingly ramshackle joint, which aims at teaching kids to play serious (and difficult) classic rock rather than contemporary fad favorites, a few are really memorable: the Collins twins, a couple of tykes with lots of enthusiasm if not exceptional talent; C.J. Tywoniak, a twelve-year old guitarist of incredible self-confidence and ability; Madi Diaz-Svalgard, a Quaker whose love of rock seems an incongruous fit with her background; and especially Will O’Connor, a gawky, brooding teen with severe emotional problems who credits the camaraderie of the place with saving him from suicide even though it hasn’t helped his playing much.

But “Rock School” isn’t actually about them, or any of the other kids, as much as it’s about Green, a voluble, loudly demanding fellow whose violent diatribes arguably verge on the abusive. The picture seems to want to portray him as a heroic figure, and his own interviews show that he certainly thinks of himself that way–as a kind of savior not only of his students but of rock itself. It’s not inappropriate, then, that the movie should take its form from the guy, mirroring him in its disheveled, rather unkempt shape and its almost chaotic, stream-of-conscious ramblings through the school and outside it–to Madi’s Quaker community in one segment (amusing, though it barely skirts condescension), for instance.

The picture does have an arc, however: it leads up to a school group’s performance at the Zappanale in Germany, where legions of Frank Zappa fans assemble each year to play his music. We’re there treated to a triumphant finale, with the kids earning cheers and congratulations even from old members of Zappa’s own band. The scene provides the picture with the note of success it needs to send viewers home happy. Unfortunately the sound recording of the concert (credited by Efrain Torres) is so substandard that it’s difficult to appreciate how well they’re playing; you have to accept the testimony of others rather than the evidence of your own ears.

“Rock School” is a picture it’s easy to be ambivalent about. On the one hand the portraits it paints of some of the youngsters–especially O’Connor and Tywoniak–are engaging, the one because it earns our sympathy and the other because it’s so simply exhilarating. Nevertheless one can’t help but find the picture it draws of Green himself somewhat disquieting. One certainly gains an understanding of why he does what he does from the brief excursions the story takes into his past and his home life, and in these segments he comes across as an amiable, if highly charged, fellow. His teaching methods, however, are so extreme–regularly employing explosive insults and obscenity-laden outbursts–that one begins to wonder whether they constitute encouragement or mere denigration. Upbraiding isn’t quite the same thing as inspiration. And since the focus of the picture is actually on him, it practically requires you to make a judgment on that–and your decision will largely determine your level of enjoyment. If your mind wanders a bit from the action on the screen, moreover, you just might find yourself wondering about the effect the single-mindedness of some of the students (the Collins twins, for instance, whose efforts seem to have the unbridled support of their mother) might have on their more traditional schooling. It’s nice to play guitar; it’s also nice to know how to read.

This picture has already been coupled with Richard Linklater’s “School of Rock,” of course–the successful comedy that had over-the-hill rocker Jack Black take a substitute teaching job in a prep school and teach his charges to play old-style rock. That was pure fiction, of course, and considerably more sentimental than this documentary, though it has to be said that in the final analysis it was also more fun. (It has to be added that in comparison to Green, the manic Black now seems almost subdued.) “Rock School,” on the other hand, has its moments, but unlike the music Green wants his students to play, it’s no classic.