Forty years after a Mississippi school district was ordered to desegregate its schools, a federal judge has finally enforced the order.

A US District Court judge in southern Mississippi has ordered the Walthall County school board to stop segregating students by allowing white students to transfer to a predominantly-white school outside of their residence area and by "clustering" white students into separate classrooms in predominantly black schools.

“The district shall cease using race in the assignment of students to classrooms in a manner that results in the racial segregation of students,” Judge Tom S. Lee said in his order, as quoted at the Christian Science Monitor. “The district shall randomly assign students to classrooms at the Tylertown Elementary Schools through the use of a student management software program.”

"More than 55 years after Brown v. Board of Education, it is unacceptable for school districts to act in a way that encourages or tolerates the resegregation of public schools," said Thomas E. Perez, head of the Justice Department’s Civil Rights Division, in a statement. "We will take action so that school districts subject to federal desegregation orders comply with their obligation to eliminate vestiges of separate black and white schools."

The Justice Department stated:

[T]he district's practice of permitting hundreds of students – the vast majority whom are white – to attend schools outside their assigned residential attendance zone without restriction prompted a disproportionate number of white students to attend a single school in the district, leaving a number of other schools disproportionately black.

Indeed, evidence in the case suggested that the community regarded certain schools in the district as "white schools" or "black schools." The United States also asserted that officials in certain district schools grouped, or "clustered," white students together in particular classrooms, resulting in large numbers of all-black classes at every grade level in those schools.

Under Judge Lee's order, students will only be allowed to transfer schools in cases of “extreme hardship or emergency.”

According to the Washington Post, 64 percent of Walthall County public school students are black, and 35 percent are white.

The county's segregation policy made the Salem Attendance Center -- the school where white students were being concentrated -- "15 percent more white" than it should have been, with 66 percent white students. Given the racial makeup of its surroundings, the school should have been 51 percent white.

Walthall County was first issued a desegregation order in 1970, but the investigation into the school's practices was closed in 2001 due to a "lack of activity."

Amanda Terkel at ThinkProgress notes that the Bush administration pulled away from enforcement of civil rights legislation, hiring civil rights staffers with "strong conservative credentials" that didn't translate into aggressive civil rights enforcement.

That appears to have changed with the arrival of the Obama administration and a promise by Attorney General Eric Holder to enact a "major revival of high-impact civil rights enforcement," as the New York Times put it.

But the Walthall County action appears to have been launched prior to the Obama administration. The Post and the CSM report that the Justice Department re-launched its investigation into the county school board in 2007, and found two violations -- the "clustering" of white students into a handful of classes and the mass transfer of students to a predominantly white school.

The county did not dispute the allegations in court.

In recent years, news reports have alleged a trend towards "re-segregation" in US schools, and the phenomenon isn't limited to rural areas in the South.

"It's getting to the point of almost absolute segregation in the worst of the segregated cities – within one or two percentage points of what the Old South used to be like," Gary Orfield, co-director of the Civil Rights Project, told the CSM in 2008. "The biggest metro areas are the epicenters of segregation. It's getting worse for both blacks and Latinos, and nothing is being done about it."