found that the Harlem Children’s Zone schools produced “enormous” gains. The typical student entered the charter middle school, Promise Academy, in sixth grade and scored in the 39th percentile among New York City students in math. By the eighth grade, the typical student in the school was in the 74th percentile. The typical student entered the school scoring in the 39th percentile in English Language Arts (verbal ability). By eighth grade, the typical student was in the 53rd percentile.
The basic theory is that middle-class kids enter adolescence with certain working models in their heads: what I can achieve; how to control impulses; how to work hard. Many kids from poorer, disorganized homes don’t have these internalized models. The schools create a disciplined, orderly and demanding counterculture to inculcate middle-class values.