Before there was School of Rock, there was Rock School, Paul Green’s Philadelphia-based music school that teaches young kids — really young, in some cases — how to play Zappa and Zeppelin. Don Argott’s documentary follows Green and his collection of oddballs and rockers as they rehearse, play gigs, and ultimately land at a Zappa festival in Germany, where they perform before thousands of hardcore Zappa fans. Green is fascinating to watch as he teaches, cajoles, and outright bullies his students into becoming rock gods, a dream he gave up on before opening his school. He alternates between goofing off with his students in the hyper style of a kid on a sugar rush and berating them for slacking off and not rehearsing their songs. A handful of his students emerge as distinct personalities, including a 12-year-old guitar prodigy and a Quaker teen whose religious beliefs get in the way of rocking out. Argott limns the school, its teacher, and its students with both genuine affection and a surprising frankness that makes this a standout documentary. These kids can really rock. (93 minutes)