Correction: An earlier version of this article had an incorrect day for when the Education Department changed its policy and misspelled the last name of Education Department spokeswoman. The spokeswoman is Dorie Nolt, not Dorie Holt. The article has also been updated to reflect Richard Kahlenberg’s role in a 2010 study of low-income children living in Montgomery County. Kahlenberg edited the study.

The Education Department on Wednesday reversed a long-standing policy and will now allow public charter schools that receive federal grants to give ­admissions preference to low-

income children, minorities and other disadvantaged students.

The move is designed to try to preserve racial diversity in schools that are attractive to wealthier families. Schools will be able to conduct a “weighted lottery” that gives preference to certain groups.

“We’ve heard from states, school operators and other stakeholders across the country that weighted lotteries can be an effective tool that can complement public charter schools’ efforts to serve more educationally dis­advantaged students,” said Dorie Nolt, a department spokes­woman.

The National Alliance for Public Charter Schools had been asking for the change for nearly three years, said Nina Rees, the group’s president.

“At the core, this brings the federal statute in line with what a lot of states have put into place to help attract more English-

language learners, special-

education students and low-

income students to charter schools,” Rees said.

In cities such as Denver, New York and the District of Columbia, a handful of well-regarded charter schools have been attracting wealthier families, making it difficult to maintain a balance between rich and poor, white and minority, said Michael Petrilli, executive vice president of the right-leaning Fordham Institute and author of “The Diverse Schools Dilemma.”

“Once the word gets out, many middle-class parents who want diverse schools end up flooding the lotteries, and then it’s not so diverse anymore,” Petrilli said. “If you can’t weight the lottery, the school ends up being predominantly white and middle class.”

Most of the nation’s charter schools are overwhelmingly low-income and high-poverty, and many aim to serve those students.

Charter schools are publicly financed but privately run, mostly with non-unionized teachers. About 5 percent of public school students attend charters; in the District, 44 percent of the city’s public school students attend charter schools.

Decades of research into school integration policies show that, on average, students learn more in schools that are economically and racially diverse than they do in segregated schools, said Richard Kahlenberg, a senior fellow at the left-leaning Century Foundation.

In 2010, Kahlenberg edited a study that tracked students living in low-income housing in Montgomery County and found those who attended integrated schools had stronger academic gains than those attending high-poverty schools.

“When charters become strong, desirable and oversubscribed, middle-class families with better access to information tend to be the ones who flood the lottery, and the composition of the school changes,” Kahlenberg said, noting that E.L. Haynes and Capital City charter schools have attracted a significant number of middle-class families.

Allowing a weighted lottery could bring some charter schools closer to the original vision conceived by Albert Shanker, the late president of the American Federation of Teachers.

Shanker proposed charter schools in 1988 as diverse laboratories of innovation that could transcend urban racial boundaries because they would draw from across a city, Kahlenberg said. But federal policy has stood in the way, Kahlenberg said, because it has required charter schools to hold blind lotteries in order to receive federal start-up funds.

To truly achieve a mix of students in charter schools, Kahlenberg said federal and state governments should allow schools to weight lotteries in favor of whatever subgroup of student is under­represented at the school. High-poverty schools could set aside seats for middle-income families, or all-black schools could make room for white, Latino and Asian students, he said.

In the past fiscal year, the ­Education Department gave $242 million in start-up funds to charter schools. The money is typically used to fund a new school during its first two years. About 1,200 schools were using the federal funds in fiscal 2013.