The expansion of charter schools in the 2000s led to an increase in school segregation and a slight decline in residential segregation, according to new research providing the first national estimates of the diverging trends.

According to the study, led by a Cornell sociologist, the average district to expand charter school enrollment between 2000 and 2010 experienced a 12% increase in white-Black school segregation and a 2% decrease in white-Black residential segregation.

The patterns moved in opposite directions, the research found, because charter schools – which receive public funds but operate independently – weaken the traditional link between neighborhood and school assignment, allowing families to choose more racially homogenous schools regardless of where they live.

The findings highlight education policy’s influence beyond schools and offer a “cautionary lesson” about continued charter expansion without efforts to limit racial sorting by families, said Peter Rich, assistant professor in the Department of Policy Analysis and Management in the College of Human Ecology.

“When school choice efforts allow parents to decide where to send their kids in an educational marketplace, school segregation increases – even if that is not the policy’s intention,” Rich said. “Whatever benefits come from the expansion of school choice should really be considered in tension with the public goal of school integration.”

Rich is the lead author of “Segregated Neighborhoods, Segregated Schools: Do Charters Break a Stubborn Link?”, published March 1 in the journal Demography. Co-authors were Jennifer Candipan, assistant professor of sociology at Brown University, and Ann Owens, associate professor of sociology and management at the University of Southern California.

Understanding charter schools’ effects on segregation is critical, the authors say, because they represent an increasingly popular educational reform. Charter school enrollment has quadrupled since 2000, serving nearly 6% of students in 2015-16, and is expected to continue growing and gaining influence.

The scholars analyzed more than 1,500 metropolitan school districts to examine what happened when school choice decoupled neighborhood and school options, using data from the census and the National Center for Education Statistics’ Common Core of Data.

School and residential segregation have historically mirrored each other, with school segregation seen as a downstream consequence of residential segregation ever since the 1954 Brown v. Board of Education decision ruled intentional school segregation unconstitutional.

Rich, Candipan and Owens said their findings reveal school and residential segregation as “more liked eddies in a stream, circling and reinforcing each other via policies and preferences.”

Previous research has shown that white families strongly prefer predominantly white schools, using race as a proxy for educational quality. In addition, some charter schools opened in Black neighborhoods of large, racially segregated city districts offer specialized curriculums and services that have made them popular choices in those communities.

As a result, the researchers wrote, some districts have essentially separate white and Black charter schools, reminiscent of older eras of legal school segregation.

“School choice gives families a little more flexibility in how they can meet both their neighborhood and their school preferences,” Rich said. “By weakening the link between where families live and where their kids can go to school, charter schools ease some of the sorting processes that typically drive residential segregation.”

The analysis did not find that charter school expansion affected white-Hispanic segregation in schools, because Hispanic students on average attend more diverse charter schools. White-Hispanic residential segregation did fall as charter enrollment grew.

Though the reductions in residential segregation were “nontrivial,” the researchers said, policymakers should not see school choice as a tool for achieving residential diversity, given how it exacerbated school segregation.

“We’d rather see neighborhood integration occur in step with school integration,” Rich said.

Moving forward, the study authors said, local school districts should adopt “diverse-by-design” policies such as weighted lotteries, controlled choice and diversity-conscious admissions algorithms to ensure that charters operate more like racially inclusive magnet schools, and federal grant competitions should reward such efforts.

Those education policies must be complemented by housing, zoning and transportation policies promoting neighborhood integration, they said, “to unleash the full promise of the Brown v. Board decision.”

“We’re in an era of race-neutral educational reform in which desegregation efforts have been slowly dismissed by courts, giving way to parents as key players in generating school segregation,” Rich said. “We should create policies that encourage parents to integrate schools rather than letting unfettered choice produce the same patterns we have tried to eliminate over the last 65 years.”