As minority populations in America’s public schools continue to climb, schools across the country are becoming increasingly segregated, according to a report released on Thursday by the Harvard Civil Rights Project.

According to the report, released to coincide with the Martin Luther King Jr. holiday, 44 percent of high schools have almost entirely black student populations, and only 14 percent of white students attend schools with significant minority numbers.

The authors points to this “resegregation” as a grave threat to the nation’s school systems at a time when 40 percent of all public school students are minorities and when, in highly multiracial areas like the south and west, that percentage increases to nearly half of all students.

“Public school enrollment in the year 2000 was more non-white than it has ever been, and black students are more segregated than they have been in the past 30 years,” said Erica Frankenberg, one of the study’s authors.

The study found that desegregation reached its peak in the late 1980s and has since rapidly retrenched.

Currently, one-sixth of the country’s black students are educated in schools that are almost completely non-white, in the northeast and midwest areas the proportion rises to one-fourth of all black students. These schools, which the report calls “apartheid schools,” often suffer from poverty, limited resources and a variety of social and health problems.

“What students need to realize is that they are living through a period like the end of the Reconstruction when rights of minorities in the country are being interpreted away by our courts,” Harvard Professor of Education and Social Policy Gary A. Orfield wrote in an e-mail, “and in which the country is moving toward greater inequality and more reinforcement of social and economic privilege.”

Orfield and the report’s other authors blame the problem chiefly on three Supreme Court decisions of the early 1990s that lowered the standards for what is necessary to be considered a desegregated school. Since that time, lower courts have found that school districts throughout the nation have met the new standard.

When desegregation laws were passed in the 1960s, school districts were forced to bus children from one part of the district to another to maintain a satisfactory level of integration in each school. The high court rulings in the early ’90s mean that schools no longer need to bus children.

Although busing met with fierce opposition in some cities, Frankenberg said that on the whole these policies worked and gained public support.

“You do see some black parents that have had to shoulder the burden of desegregation, but you also see a growing acceptance of desegregated schools in the public opinion,” she said.

Frankenberg said she has experienced the phenomenon she and her colleagues call resegregation. She attended a public high school in an Alabama school district where a desegregation court order was lifted. In her senior year, the district redrew the boundary lines that determine where students went to high school.

“The white neighborhood was taken away from the school, so the black population got bigger,” she said.

The report found that Latinos suffer the most of any minority, as they are the most segregated group and also maintain the highest levels of linguistic separation and dropout rates.

At the other end of the spectrum, Asians are the most integrated of all minority groups and enjoy the least amount of linguistic separation. The report did not distinguish between different Asian nationalities, but it found that as a whole the college graduation rate for Asians is nearly double the national average—and four times greater than the college graduation rate for blacks.

Frankenberg said no factor can precisely determine why Asians have had such success interacting with other races but said she believes it may have to do with the size of the Asian population in the United States.

“Some scholars suggest that when a minority is smaller, it is easier to bring into society,” she said. “Boston has schools that are 15 to 20 percent Asian, but it is nothing like what we see with Latino students.”

The study did not research universities in any capacity, but Frankenberg said she feels there will be repercussions for universities nationwide.

“What it means for colleges like Harvard is that students who are coming from more segregated schools are going to be less exposed to students of other races,” she said.

—Staff writer Douglas G. Mulliken can be reached at mulliken@fas.harvard.edu.