Taken from a larger study about life in high school classrooms from students' perspectives, this paper discusses how study participants pinpointed individual classrooms as the nerve centers in students' high school experiences. Punctuating the swirls of movement within school days, individual class periods contain clues about how students construct knowledge and meaning in school. Nested within classrooms period to period, participants reported being tangled in webs of peer influence that variously encourage, constrict, poison, and otherwise determine students' classroom interaction. Each 42-minute class period or classroom episode necessitates that students perform a kind of double-duty as they strike appropriate academic and social poses not only for their teacher but--much more importantly--for their peers, who create classrooms that can be comfortable, indifferent, or perilous to students. Once inside individual classrooms, students work hard to follow tacit codes for appropriate behavior among assembled peers. Although this unspoken but de facto student culture can differ period to period, it nevertheless dominates students' experience of school. Because this finding reveals so much about students' social compromise and so little about their engaged learning, it seems that classroom teachers hold the surest, most immediate power to reclaim and reform classrooms from sites of student accommodation to sites of active and even enjoyable accomplishment.