The twist that makes this somewhat ragged comedy work as well as it does is that the two cops revert to the level of high-school immaturity as they blend in with the genuine teens around them. Former nerd Hill is especially susceptible, as he is determined not to relive his uncomfortable past.
21 Jump Street goes for easy laughs wherever possible, raunchy or otherwise, in Michael Bacall’s screenplay (with a story co-credited to Hill) but the likability of its stars carries it a long way. Tatum turns out to have a sense of humor about himself, which comes as a pleasant surprise, and holds his own alongside his cohort. The film isn’t long, but it runs dry at a certain point, and tries to rescue itself by morphing into an action movie, with only middling results.
Still, I suspect that its target audience will feel they’ve gotten their money’s worth in this amiable and irreverent comedy, which makes fleeting nods to the 1980s TV show that spawned it.