There's no disputing that many of Minnesota's public charter schools lack racial diversity. Because some of them were started specifically for underserved, disadvantaged students, they enroll a majority of low-income kids of color.

Now an updated local study shows that the number of charter schools serving predominately white children is growing in the Twin Cities. A survey by the Institute of Metropolitan Opportunity at the University of Minnesota Law School found that those charters in suburbs grew by 40 percent in the last five years. Authors of the report say the schools feed "white flight" from diverse, traditional suburban public schools in cities such as Bloomington and Eden Prairie.

The bigger question is whether this kind of segregation is good or bad for students and for society overall. What's more important — improving student achievement, no matter what the racial balance in the school, or mandating that all schools have a specific racial mix?

Diversity in schools is worth striving for. Given that today's young people will become adults in a more diverse world, it would be preferable for all students to attend schools that are racially and socioeconomically mixed.

However, given the current learning disparities between white students and lower-income students of color, it is imperative to use a variety of strategies to narrow those gaps — including those being used in some schools with predominately one race.

A few charter schools that work with mostly African-American or Asian or Hispanic students have significantly improved achievement and should continue that good work. If charter schools — and traditional public schools, for that matter — fail students year after year, they should be closed or reconstituted.

It's important to remember that there's a huge difference between school segregation in the middle of last century and what happens today. Federal court rulings in the 1950s overturned segregation that was legally required under state and local government rules. That legal segregation also produced schools with vastly unequal resources and facilities for black and white children.

Today, many urban public schools have become resegregated largely because of housing patterns based on where people either choose to live or must live because of their incomes. Contemporary inner-city schools have high percentages of students of color because their families are disproportionately poor. And when more white families moved to the suburbs, fewer white children remained in many cities to attend traditional public schools.

When public charter schools began two decades ago, many were created especially for students who were not doing well in traditional public schools — many of them students of color. Over the years, parents have sent their children to charters voluntarily for a variety of reasons: stronger academics, a language focus, teaching methods, a welcoming atmosphere or location.

At the same time, public charter school funds should not be used to create elite private schools.

That's why Minnesota's leaders should consider striking a better balance. Last year, legislation was introduced by Sen. Terri Bonoff, DFL-Minnetonka, that would allow all charters to give admissions preference to students who are eligible for free- and reduced-price lunches. Some other states allow such preferences to bring more diversity to charter schools.

Lawmakers also could consider involving charters in voluntary partnerships with other schools. That wouldn't create quota or admissions targets, but it might offer incentives for both closing the achievement gaps and promoting cross-cultural and racial understanding. In addition, policymakers should consider housing incentives that would increase affordable housing in suburban areas.

Although mandating a specific racial mix for charter schools would be a mistake, encouraging voluntary diversity in successful charters is a worthy effort.