If the Iowa City Community School District passes the proposed plan to diversify schools, it will join more than 80 districts across the nation that have responded to research on student achievement by giving more students the chance to attend mixed-income schools.

Research shows that while students’ own socioeconomic backgrounds have a big effect on their achievement, so do the socioeconomic backgrounds of their peers. Numerous sources — including the famous 1966 Coleman Report, data from the National Assessment of Educational Progress, and a 2010 meta-analysis by researchers at the University of North Carolina at Charlotte — show that poor students at mixed-income schools do better than poor students at high-poverty schools.

In their recent guest column opposing the plan, Tuyet Dorau and Michael Shaw argued that this relationship is correlational not causational, and suggested that the connection between school poverty levels and academic achievement “is no more significant than the relationship between taking the city bus and poor student achievement.” Dorau and Shaw argue that instead of focusing on student composition, the district should focus on the resources they are providing schools.

We disagree.

Although there is no reason to believe that taking a city bus reduces achievement, there are three powerful reasons to believe that attending a high-poverty school does.

• First, extensive research finds that, on average, mixed-income schools have higher quality teachers than high-poverty schools because the working conditions are seen to be better. Efforts to lure excellent teachers to schools with concentrations of poverty are likely to be ineffective unless an enormous wage premium — on the order of 40 percent — is provided.

• Second, mixed-income schools generally have more involved parent communities than high-poverty schools. Because middle-class parents are more likely to have the time and resources to volunteer in class and become involved in school affairs, they can be effective advocates for all children in mixed-income schools. For example, research finds middle-class parents are four times as likely to be members of the PTA as low-income parents.

• Third, one of the biggest advantages of attending a socioeconomically integrated school is having peers who are more likely to be high-achieving and highly motivated than peers at a high-poverty school. Middle-class students come to school, on average, with about twice the vocabulary of low-income students, are more likely to have access to outside resources such as libraries and museums, and are more likely to come from families with higher educational aspirations for their children. These are important benefits for all students in a mixed-income school, since high-achieving students can help teach other students, and motivation can be contagious.

It is possible to make high-poverty schools work; we all know of isolated examples. But only 1.1 percent of high-poverty schools meet a standard of consistent high performance, according to 2005 calculations by economist Douglas Harris.

What about the proposal to try to improve economically segregated schools with greater resources?

A 2010 Century Foundation study tested the very question of which helps low-income students more, attending a higher poverty school with more resources or attending a lower poverty school without extra resources, and found that lower poverty, not extra resources, increased achievement. Researcher Heather Schwartz looked at outcomes for public housing students who were randomly assigned to housing units, and corresponding school attendance zones, throughout Montgomery County, Md.

Those public housing students assigned to the most-advantaged schools performed significantly better than those who attended the least-advantaged schools, despite the fact that the county provided the least-advantaged schools with extra resources, including reduced class size, increased professional development, and increased math and literacy instruction.

Dorau and Shaw also object to Iowa City’s focus on income rather than race, but there are two reasons policymakers across the country have made this shift. First, a 2007 U.S. Supreme Court decision, Parents Involved v. Seattle School District, struck down a racial integration plan as unconstitutional, but using socioeconomic status remains perfectly legal.

Moreover, research suggests that if one’s goal is to raise academic achievement, the economic mix in a school is even more important than the racial mix. Having said that, one of the attractions of socioeconomic integration is that it often produces racial integration indirectly — a positive benefit for all school children.

Socioeconomic integration is one of the most effective ways to help boost the achievement of low-income students, and Iowa City — with a majority middle-class population and a wealth of cultural resources — is especially well positioned to implement such a policy.

If the district decides to use magnet schools to help reach the diversity goals — perhaps partnering with the University of Iowa to create new programs in areas such as language immersion, STEM or music — the results of the diversity plan could create exciting new options for families of all socioeconomic backgrounds.

Richard D. Kahlenberg is a senior fellow, and Halley Potter a policy associate, at the Century Foundation, a public policy research organization with offices in New York City and Washington, D.C.