Black and Latino children are becoming increasingly segregated from their white classmates in American schools, a Harvard University study has found.

Almost 50 years after a US Supreme Court ruling outlawed racial segregation in schools, nearly all the schools studied are now "re-segregating".

The study says two factors - poverty and government policy - are to blame for the increasing racial gulf.

The worst cases of segregation were still to be found in the southern states, where the most bitter civil rights battles were fought in the 1950s and 1960s.

Little contact

Harvard's Civil Rights Project studied 185 of the largest school districts over a period of 14 years.

It set up an "exposure index" to look at the pattern of how many black and white students came into contact with one another.

In the worst case of re-segregation, in Clayton County Georgia, black exposure to whites dropped from 68.7% in 1986 to 23.1% in 2000.

That means the average black student now goes to a school where only 23.1% of his classmates are white.

Overall, the study found:

• Black exposure to whites only increased in four of the 185 districts
  
• Latino exposure to whites only increased in three districts
  
• White isolation from blacks increased in 53 districts.

Integration unravelled

The study's author, Chungmei Lee, said people had become discouraged about integration.

In the 1950s desegregation laws had to be imposed by force

"I think a lot of people think that nothing can be done, and the efforts have failed," he said.

Several court rulings have forced affirmative action plans to be scrapped for being unconstitutional.

"As courts across the country end long-running desegregation plans and, in some areas, have forbidden the use of any racially-conscious student assignment plans, in the last 10-15 years there has been a steady unravelling of almost 25 years worth of increased integration," said Harvard's Professor Gary Orfield.

The study's authors believe integration is crucial to improve education and prepare students for life in a diverse culture.

Divided diversity

The 2000 census results showed that the US has more racial diversity than ever before.

But minorities often live in poor neighbourhoods, which contributes to the racial divide in schools.

The report recommends combining inner city and suburban school districts to bring children from different communities together.

But campaigners against desegregation warned against seeing diversity as automatically being a good thing.

"When you have a government involved in enforcing a particular form of diversity, then you have a government making decision that are illegal," said lawyer Chester Darling.