More than 60 years ago, the courts deemed school segregation unconstitutional, yet across the country many students still attend school primarily with students who look like them.

Research shows that the racial composition of the public school student population has changed substantially over the past 25 years, but student racial sorting among schools has remained relatively stable. A growing body of research shows that school segregation matters for the educational and socioeconomic outcomes of students of color. To fix it, however, we have to understand why racial segregation has persisted.

School segregation is a complex problem, rooted in history, structural racism, school assignment policies, and parental behavior. In this piece, we focus on one lever that captures many of those factors: residential segregation.

The chart above compares the residential segregation of school-age kids in a city with the segregation at public and most private schools in that same area in 2015. For the purposes of this piece, we consider the segregation of black or Hispanic students from their peers from other racial and ethnic groups.

Our segregation measure ranges from zero to one, with zero representing a perfectly integrated city in which each neighborhood or school is representative of the racial composition of the city or school system and 1 corresponding to a perfectly segregated world in which there is no interaction across racial groups at all. This index measures how far away the system is from being perfectly segregated, in proportional terms. A segregation level equal to 0.3, for instance, means the city is one-third as segregated as the maximum it could be given its racial composition. If residential integration were the only determinant of school integration, we’d expect cities to fall right on the 45 degree line. Where does your city land?