The Civil Rights Project at Harvard University found integration between whites and blacks to be decreasing or steady in all but a handful of the nation's largest school districts over the last 14 years.
The report's authors say the "re-segregation" trend is a result of recent court rulings that dismantled race-based desegregation laws, and also reflects discouragement over stalled integration efforts.
"I think a lot of people think that nothing can be done, and the efforts have failed," said Chungmei Lee, a co-author of the report.
Lee said integration is crucial to improve education and prepare students to live in a diverse culture.
Attorney Chester Darling, who represents parents fighting a desegregation policy in Lynn, Mass., questioned the study's assumptions about diversity's value. He also said any new push to create school diversity must be driven by parents and not government.
"When you have a government involved in enforcing a particular form of diversity, then you have a government making decisions that are illegal," he said.
The report measured the changing "exposure index" between races in school districts with enrollments larger than 25,000. For instance, a black-white exposure index of 23 percent means the average black student attends a school where 23 percent of the students are white.
In a sample of 185 of the districts, black exposure to whites increased in only four of the districts between 1986 and 2000. Latino exposure to whites increased in only three districts. White isolation increased in 53 districts, the report said.
The study found re-segregation to be the most rapid in Clayton County, Ga., where the average black student goes to a school that is 23.1 percent white, down from 68.7 percent white in 1986.
The 20 most rapidly re-segregating school districts are concentrated in the South, with eight in Texas and three in Georgia.
But the most stable districts are also in the South, the report noted, in what it said might be a lingering effect of defunct integration plans that were once heavily concentrated in the South.
Lee said successful integration is simply a matter of balancing resources, which are often in short supply in the poor neighborhoods where many minorities live. The report recommends combining city and suburban school districts into one entity, joining various racial groups in the process.
Rich Kahlenberg of The Century Foundation, a New York-based think tank, said communities need to focus on income disparities if they want to legally desegregate.
"People are stuck in the old paradigm of race," he said. "But that's outmoded because we have some new legal realities to deal with."
By Jay Lindsay