After the U.S. Supreme Court declared separate public schools for black and white students were unconstitutional in the landmark 1954 Brown v. Board of Education of Topeka ruling, some whites in the South resisted by opening private schools or by creating white-only public school districts.

For nearly two decades, a new school secession movement has been growing — and it’s not only in the South. I ran a post last year about this, and here is a new look, with a discussion about the consequences for U.S. students.

This report comes from a newsletter produced and published by the National Education Policy Center at the University of Colorado at Boulder. The center produces high-quality, peer-reviewed research to inform education policy discussions and issues critiques of research published elsewhere. This was published on the center’s website, and I was given permission to publish it.

Here’s the report from the National Education Policy Center:

In 2014, six suburban towns seceded from Shelby County Schools, the school district that includes the city of Memphis, Tennessee.

One year later, the rapidly growing, semirural suburb of Pike Road seceded from Alabama’s Montgomery Public Schools, building separation from the city that Martin Luther King, Jr. began calling home in 1954.

Meanwhile, in East Baton Rouge Parish, Louisiana, three secessions occurred between 2000 and 2010, and a fourth is pending.

The secessions are part of a trend of neo-segregation in which predominantly white and relatively affluent areas divorce themselves from school districts that are majority-minority and have greater poverty. In total, 47 occurred between 2000 and 2017 in 13 counties, seven of which are located in the South.

In a study published this month in the peer-reviewed journal AERA Open, Kendra Taylor of Sanametrix, and National Education Policy Center Fellows Erica Frankenberg (Pennsylvania State University) and Genevieve Siegel-Hawley (Virginia Commonwealth University) examine how the secessions affected racial segregation in these seven counties.

They find that, on average, the secessions increased the proportion of racial segregation attributed to school district boundaries (as opposed to segregation between schools). For instance, in 2000, an average of 60 percent of black-white segregation was attributable to school district boundaries. By 2015, this figure had grown to 70 percent.

During that same period, the school districts themselves grew less diverse than the counties in which they were located. This is notable in part because earlier desegregation efforts the South had greatly benefited from its large, countywide school districts.

In contrast, desegregation efforts in the North — where district boundaries usually stopped at the city line and where designers of sprawl created white suburban enclaves — faced daunting legal barriers because court orders generally could not cross district lines.

In their new study, Taylor, Frankenberg and Siegel-Hawley also find that systems in which secessions occur enroll smaller shares of white students (33 percent) than does the average school district in the South (43 percent). The separations led to increasing rates of residential segregation in the counties with the most extensive patterns of secession.

Nationwide, more than 120 communities have attempted to secede from their school districts since 2000, as found in a 2017 report by the nonprofit EdBuild.

“If this trend continues, students of color increasingly will be sorted into schools with fewer resources, segregation will become more ingrained, and all students will have fewer opportunities to experience the educational benefits of a diverse learning environment,” Frankenberg told CBS News.