Greg Jacobs and Jon Siskel's documentary doesn't sound promising. Here's another film following a bunch of contestants through the rounds of a tense competition, and the contest itself, the Louder Than a Bomb poetry slam, is also on the edge of dubious. How many of these Chicago high-school students perform "real" poetry, or is it all raw amateur stuff, rhetorical and melodramatic monologues? Somehow, the objections melt away. The formula is reinvigorated, as the competition gets undeniably exciting. That's because the kids whom Jacobs and Siskel have chosen for us to watch are so enthralling, with such remarkable life stories, that their autobiographical poems have actual power. Especially compelling is the story of the inner city team from Steinmetz Academic Center: undisciplined, unruly, and strikingly talented. A long scene in which three kids beg not to be thrown off the team for being disrespectful to their teachers is an astonishingly moving episode of classic cinema vérité. (Director Greg Jacobs will introduce this weekend's screenings of Louder Than a Bomb at the Coolidge.)