Low-income students 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 new study 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 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 County, Md., 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, 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.”