A model of the effects of economic level and ethnicity on grade 8 mathematics scores both within and between schools found that both the economic composition and the ethnic composition of a school were directly related to the effectiveness of that school. Projection of the data suggests that if the nation's schools were completely desegregated economically (but not at all ethnically), the test-score gap between free lunch students and students paying full price for lunch would decline by 25 %. Ethnic compositional effects for black, Asian/Pacific Islander (API), and Hispanic students were reversed from their within-school effects, with positive effects for students in schools with larger proportions of black and Hispanic students and a strong negative effect for students in schools with larger proportions of Asian/Pacific Islander students.