While US schools are growing more diverse, they remain highly segregated by race and class, according to a new analysis.

More than a third of students in the US attended racially segregated schools – schools in which more than three-quarters of students accounted for one race or ethnicity, according to an analysis of 2020-21 Common Core education data by the US Government Accountability Office. What’s more, more than one in 10 students – 14% – attended schools where 90% of students were of one race or ethnicity.

The report, released Thursday, comes just six years after the agency found a stark increase in the percentage of poor, Black and Latino students attending predominantly poor and minority schools over the course of a decade and a half. It also comes decades after the US supreme court declared “separate but equal” schooling unconstitutional in the landmark case Brown v Board of Education – a promise which remains unfulfilled for millions of America’s children.

“We pay homage to the idea of Brown but I don’t think, in terms of policy at the federal level, we have supported even voluntary efforts that would support voluntary efforts that would facilitate integration,” said Erica Frankenberg, a professor of education at Penn State University who has studied segregation in America’s schools.

While Black students accounted for 15% of the US public school population, 23% of them attended schools that were more than three-quarters Black. By comparison, 43% of white students, who now make up less than half of the US school population, attended predominantly white schools, nearly double that of Black students. For Latino students, who accounted for 28% of the US school population, 31% attended predominantly Latino schools.

The majority of schools in the midwest and north-east, which also had the highest percentage of schools that were predominantly a single race, were majority white. By comparison, schools in the west had more predominantly Latino students, while the south had more schools with largely Black and Latino students than other parts of the country.

US government officials highlighted two contributing factors to the continued segregation of America’s children: school district boundaries that determine who has access to what schools and the rise of school district secessions – the phenomenon of towns breaking away from larger school districts to establish their own school districts.

Frankenberg says that past supreme court cases have undermined efforts to desegregate school districts and the steps the federal government can take to integrate schools. In 1974, the supreme court’s ruling in Miliken v Bradley, which focused on schools in the Detroit area, established that school districts were not responsible for desegregating across district lines and, Frankenberg says, “really made district boundaries set the boundaries for what kind of desegregation could occur”.

School funding also often relies on local property taxes and students often attend schools close to where they live, creating unequal access to resources when communities are segregated. What’s more, a separate landmark case in 2007 over Seattle’s desegregation efforts limited what voluntary integration efforts could be taken.

“It’s been many decades since we’ve had all branches of the federal government working on this problem,” she says.

The GAO report found that between the 2009-10 and 2020-21 school years, more than 30 new districts broke off from previous school districts in seven states. Districts that broke from larger ones became wealthier and less racially diverse than the districts left behind, while the percentage of students on free or reduced lunch – a proxy for poverty – was sliced in half.

“Compared to remaining districts, new districts had, on average, roughly triple the share of White students, double the share of Asian students, two-thirds the share of Hispanic students, and one-fifth the share of Black students,” the GAO report noted.

“Boundaries are seen as invisible structures that you can’t do anything about. Secession is the creation of new boundaries. You can prevent the formation of them,” Frankenberg, who has studied secession efforts, says. “The question is, what is going to be the federal government [approach], if any, to try to address the way in which [boundaries] are having a disproportionate effect on race and class?”

Congressman Bobby Scott of Virginia, chair of the House education and labor committee, called on Congress to pass legislation that would send funding to schooldistricts and states to devise plans to voluntarily integrate schools and “address policies and practices that have a discriminatory impact on students”.

“We know that school segregation doesn’t just isolate low-income students and students of color; it also deprives them of equal access to educational opportunities and resources,” Scott said in a statement. “We simply cannot allow our progress toward educational equality in America to be further eroded.”