Mary Ann Zehr:

A growing number of school districts are trying to break up concentrations of poverty on their campuses by taking students’ family income into consideration in school assignments.
Some of the districts replaced race with socioeconomic status as a determining indicator after the U.S. Supreme Court ruled in 2007 that using race as the primary factor in assigning students to schools violates the Constitution. Other districts that take family income into account never included race as a factor.