During her elementary school years in this rural Mississippi town, Addreal Harness, a competitive teenager with plans to be a doctor, said her classes had about the same numbers of white and black students. It was a fact she took little note of until the white kids began leaving.

Some left in seventh grade, even more in eighth, and by the time Harness, who is African American, reached Tylertown High School, she became aware of talk that has slowly seeped into her 16-year-old psyche -- that some white parents call Tylertown "the black school," while Salem Attendance Center, where many of her white classmates transferred, is known as "the white school."

"In my class of 2012, there's just seven white girls now," said Harness, raising her chin slightly. "The ones that left, they think Salem's smarter because they have more white kids, but it's not."

Last week, a federal judge ruled that a school board policy here in Walthall County has had the effect of creating "racially identifiable" schools in violation of a 1970 federal desegregation order. Although the case is unique in some ways, it fits a broader trend toward racial isolation that has been underway for years in American schools and has undermined the historic school integration efforts of the civil rights era.

More than half a century after courts dismantled the legal framework that enforced segregation, Obama administration officials are investigating an array of practices across the country that contribute to a present-day version that they say is no less insidious....

The Walthall County case fell under the jurisdiction of the Justice Department, which is still monitoring more than 200 mostly Southern school districts for compliance with desegregation orders dating to the 1960s and '70s. Justice officials said they have sometimes found that local school boards have adopted policies that undermine those orders, a situation that some experts say reflects a misguided sense that civil rights concerns are somehow a thing of the past.

Studies have shown schools drifting back into segregation since the 1980s, when the federal government became less aggressive in its enforcement. The Supreme Court ruled in 2007 that school districts cannot make racial balance a policy goal unless -- as is the case in Walthall -- they are attempting to comply with a federal desegregation order.

"School boards are constantly under pressure from privileged parts of their districts, and if there isn't any counterbalance of civil rights enforcement policy, you can easily end up with a set of decisions that increase segregation," said Gary Orfield, director of the civil rights project at the University of California at Los Angeles. Its studies that show that 38 percent of black students and 40 percent of Latino students attend public schools that are more than 90 percent minority....

"We said we're going back to where it was before 1970," said Clennel Brown, who heads the local NAACP branch that complained to the Justice Department. "When the white parents say 'more comfortable,' to me it's saying 'I don't want my child to be influenced by black children.' "...