Tomorrow, May 17, will be the 60th anniversary of Brown vs. Board of Education, the Supreme Court case that marked the beginning of the end for school segregation. Thanks in part to Brown, most people today think of single-race schools as a vanquished instrument of racial discrimination. The case itself has entered American legend: even grade-schoolers learn that "separate but equal" is a failed idea, abandoned long ago.

But in the Twin Cities, many of those grade-schoolers are sitting in segregated classrooms. Single-race schools have been making a comeback in Minnesota.

It's the charter schools that are the problem. Charters are rapidly growing, but still controversial, with their effectiveness hotly debated. Despite that controversy, or perhaps because of it, a disturbing reality about charters is widely overlooked: Many boast student bodies that are entirely composed of members of one race.

Nonwhite students are particularly isolated. Over half of local charters are minority-segregated. If you're an African-American student at a charter school, there's an 88 percent chance your school is segregated. The figure is similarly high for Hispanic students (76 percent) and Asian-American students (82 percent). White students are also increasingly affected: the chance that they'll land in a white-segregated school has risen from 56 percent in 2000 to 73 percent today.

This degree of separation is unjustifiable in a region that's only 24 percent nonwhite, and where the majority of other public schools are integrated. It's not just a question of geography, either — more than a dozen suburban charters are proportionately whiter than other nearby schools, and the central cities feature more than a half-dozen white-segregated charters located near nonwhite-segregated charters.

It gets worse: As some parents and students abandon traditional schools for single-race charters, traditional school systems face pressure to create similar enclaves. Incredibly, this corrosive process has led to the re-emergence of explicitly segregated traditional public education. For instance, Minneapolis public schools caved to parental pressure and opened the Hmong International Academy, intended as an alternative to the now-primarily-black Lucy Stark Laney Elementary — effectively steering each student body into institutions made up of "their own" racial group.

Until recently, such open segregation would never have been allowed under Minnesota law. In order to accommodate charters and their spillover effects, the state has had to gut its desegregation rules, replacing them with a system in which "racially identifiable" schools are allowed to persist with minimal pressure to integrate. Charters are also exempted from the state's broad desegregation plan and, in 2001, the state changed the law to allow students to enroll in a charter without consideration of the effects on integration.

We can't allow new ideas about education to erode civil rights progress. There is, after all, nothing truly new about the practice of concentrating minorities in substandard schools. Right now, school choice too often means the choice to separate from other races. Brown's justices would have surely found this systemic racial sorting deeply troubling, no matter the mechanism behind it.

Charter advocates frequently insist on the need to close the equity gap and create opportunity for all students, no matter their race. But their commendable agenda cannot proceed in a segregated organization. As we celebrate Brown's legacy, we should also remember its lessons: that integration is the grandfather of all equity issues and that racial separation is a root cause of American inequality.

As publicly funded entities, charters have a moral obligation to repudiate segregation. The state has a moral obligation to enact rules that end the racial seclusion of its children. Charter schools should not allow themselves to become flagbearers for a divided system reminiscent of an uglier era.

Will Stancil is a researcher at the Institute on Metropolitan Opportunity at the University of Minnesota.