Slightly formulaic, but still amusing, School Of Rock is exactly what you might expect.
The plot focusses around Jack Black trying to teach some school kids to rock. You know what to expect, he helps a few of them through hard times in their life, and helps them to loosen up. They, in turn, teach him to grow up.
Despite the predictable, back of a matchbox script, it is still fairly amusing. This can be attributed more to the charm and energy that Black puts into his perfomances, than to the jokes themselves. Either way, though, it is well worth watching.