Most educational reform programs, including No Child Left Behind, operate from the perspective that gaps in academic achievement can be reduced by improvements in the educational process directed by school administrators and teachers. This perspective ignores the ecological context in which underachieving schools are typically embedded. Using a developmental approach, we show that school-wide achievement of elementary school children in New York City, the nation's largest public school system, is better characterized by the accumulation of multiple risk factors within schools and within the neighborhoods where they are situated. School risk factors include teacher experience, teacher and student mobility, teacher absences, and school building quality. Neighborhood risk factors include proportion in poverty, parental educational attainment, proportion of single parents, housing quality, residential crowding, and neighborhood deterioration. Cumulative risk within each of these ecological domains, as well as their interaction, is significantly associated with school-wide achievement. (Contains 1 figure and 3 tables.)