Protesters get up and shout ‘hey, hey, ho, ho, resegregation has to go’ after the Wake County, N.C. school board voted in 2010 to end the county’s diversity-based assignment policy. (Photo by Ethan Hyman/News Observer)

Race-based school integration plans helped boost black students’ achievement after Brown v. Board of Education, but those plans fell out of favor in recent decades as districts persuaded courts that they had moved beyond their separate-but-equal past.

The result in many places? A system of resegregated schools.

But in a small number of school districts, officials are trying a different approach, assigning children to school based in part on their family’s income. And when poor kids mix with richer kids in class, they tend to do better academically, especially in math, according to a new study of large North Carolina school districts that was published in the journal Urban Education.

The researchers examined Wake County, the only one of North Carolina’s largest districts that replaced its race-based school assignment plan with an effort to integrate schools by family income. The move caused a furor in Wake County, where voters ousted some school board members because of the plan.

“I was curious as to whether it had much of an effect, since people were so upset about it,” said William A. Darity Jr., a professor at Duke University and co-author of the study. “Our answer is: It doesn’t do as well as the race-based plan in terms of producing higher levels of diversity. But it does appear to have some benefit for student performance.”

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Adopted in 2000, the plan said that no more than 40 percent of children in a school should be low-income, as measured by free lunch eligibility, and no more than 25 percent should be performing below grade level on state tests.

The state’s other four largest districts were less aggressive about trying to maintain diversity. Generally, they assigned children to schools based on their home address, with some opportunity to attend choice-based programs in other neighborhoods.

Wake’s schools became slightly more segregated between 2001 and 2009, but nowhere near as segregated as they would likely have been without the socioeconomic diversity plan, according to the study. And unlike in the other districts, the achievement gap between white and black students narrowed in Wake County, with black students’ test scores showing the equivalent of an extra 23 to 27 days of learning, according to Monique McMillian of Morgan State University, the study’s lead author.

The new work doesn’t explain what it is about mixed classrooms, exactly, that makes a difference for students. But it adds to a growing body of research that is helping to drive interest in using socioeconomic integration to improve academic outcomes, said Richard D. Kahlenberg, a senior fellow at the Century Foundation who was not involved in the research.

Kahlenberg said two decades ago, only one school district in the nation — in La Crosse, Wisc. — was trying to integrate along socioeconomic lines. Now there are more than 80 districts that serve about 4 million students doing so, he said.

“Two decades of trying to make separate but equal work have been frustrating to a lot of school leaders, and so they’re looking for new approaches, and socioeconomic integration is one of the most powerful interventions available,” Kahlenberg said. “This study suggests that if we’re looking at academic achievement, socioeconomic integration is the more powerful lever, as opposed to racial integration.”

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Kahlenberg said that some school districts have shown that it’s possible to integrate schools smoothly, in a way that parents can accept. But Wake County is still grappling with the political fallout that accompanied its effort to mix rich and poor kids in school.

In 2010, a new majority-Republican school board backed by tea party conservatives voted to do away with the integration plan, calling it an attempt at social engineering. A year later, a Democratic majority took office, but it did not restore the old plan; now, income plays a role — but a small one — in Wake County school assignments.

And schools in Wake County have become more segregated, as the Raleigh News and Observer reported in August:

In the past seven years, the number of high-poverty schools in Wake has increased by more than 150 percent. Schools where at least half the students received subsidized lunches numbered 18 in 2008; last school year, there were 46, more than a quarter of Wake’s schools. Also, since 2008, the number of schools where at least 70 percent of the students are receiving subsidized lunches has gone from none to 12.

Additionally, 24 Wake schools have populations where black and Hispanic students make up at least 70 percent of the enrollment, compared with 12 schools in 2008. During that period, black and Hispanic enrollment has increased by 3 percentage points to 41 percent.