When teachers heard footsteps thundering in the hallways at Adlai E. Stevenson High School in the Bronx, they threw down iron gates to stop student gangs from rioting, even as other students tried to deconstruct literature behind locked classroom doors. A decade ago, Stevenson, in the borough’s Castle Hill section, was one of the city’s most dangerous, overcrowded schools, barely containing its 3,054 students — when they showed up for class.

