Low-income students in Montgomery County performed better when they attended affluent elementary schools instead of ones with higher concentrations of poverty, according to a new study that suggests economic integration is a powerful but neglected school-reform tool.

The debate over reforming public education has focused mostly on improving individual schools through better teaching and expanded accountability efforts. But the study, to be released Friday, addresses the potential impact of policies that mix income levels across several schools or an entire district. And it suggests that such policies could be more effective than directing extra resources at higher-poverty schools.

The idea is easier to apply in areas with substantial middle-class populations and more difficult in communities, such as the District, with large concentrations of poverty. Yet it lends fresh support to an idea as old as the Supreme Court's Brown v. Board of Education ruling in 1954: Segregated schools - in this case, separated by economics, not law - are rarely as good as diverse ones at educating low-income students.

"Today, 95 percent of education reform is about trying to make high-poverty schools work," said Richard Kahlenberg, senior fellow at the Century Foundation, a progressive think tank based in New York that published the report. "This research suggests there is a much more effective way to help close the achievement gap. And that is to give low-income students a chance to attend middle-class schools."

The study tracked the performance of 858 elementary students in public housing scattered across Montgomery from 2001 to 2007. About half the students ended up in schools where less than 20 percent of students qualified for subsidized meals. Most others went to schools where up to 60 percent of the students were poor and where the county had poured in extra money.

After seven years, the children in the lower-poverty schools performed 8 percentage points higher on standardized math tests than their peers attending the higher-poverty schools - even though the county had targeted them with extra resources. Students in these schools scored modestly higher on reading tests, but those results were not statistically significant.

"The conventional wisdom - and I don't want to knock the foundation of it - is that we really need to infuse the poorest schools with lots of resources," said Stefanie DeLuca, associate professor of sociology at Johns Hopkins University, who has studied the issue and read an advance copy of the report. "This study turns that wisdom on its head to some extent. It says, actually, it's who you are going to school with."

Independent researchers call the report a step forward in studying the benefits of economic integration, which has been difficult to measure because it is hard to find large numbers of poor kids in wealthy areas. But Montgomery provided an ideal laboratory because of a long-standing policy of requiring developers to set aside housing for low-income families, who win spots through a lottery.

That randomness strengthens the study, researchers say. It mitigates a problem that hampered previous studies in which parents actively chose to place their children in better schools, making it difficult to separate the effect of the schools from the effect of having motivated parents.

Researchers see the results as especially significant because Montgomery, one of the nation's best and largest public school districts with 144,000 students, has been uncommonly aggressive in seeking to improve the performance of students in schools with higher poverty.

It has divided the county into a high-performing, more-affluent green zone and a high-needs red zone, where schools receive about $2,000 more in per-pupil funding. And yet, the low-income students in the study performed better in the green-zone schools.

Montgomery School Superintendent Jerry D. Weast said that the report's findings were no surprise but that his policies are designed to counteract the ill effects of housing patterns that concentrate poverty in certain areas.