Bokura no Nanokakan Sensou

The mystery story and social satire begins on the day before summer vacation, when every boy in a first-year class of a downtown Tokyo middle school disappears. Was it some accident? A mass kidnapping? Actually, the boys holed themselves up in an abandoned factory on the riverbed. With support from the schoolgirls, the boys start a revolution against the adults from this "liberation zone."
(Source: Anime News Network)