We analyze the relationship between residential populations, school attendance zone boundaries (AZBs), and school enrollments in two large, countywide suburban districts, Fairfax County, Virginia, and Montgomery County, Maryland, from 1990 to 2010. A steep decline in white, school-age children and an increase in black, Hispanic, and Asian children in both neighborhoods and the schools that serve them suggests that white households reluctant to send their children to diversifying schools are exiting (or never entering) these districts entirely rather than sorting within them. AZB changes, often due to the opening of new schools, affect a large portion of both districts, but boundary changes are associated with only a small portion of increased segregation observed in both schools and neighborhoods between 1990 and 2010. Our findings speak to the complex, multidirectional relationships between demographic trends and AZBs in diversifying, growing suburbs.