A new study looks at charter school segmentation in North Carolina based on racial and income demographics. The kids pictured here are at a New Orleans charter school in 2007. Getty / Mario Tama A new paper from three Duke University researchers studied the North Carolina charter school movement and came to a disturbing conclusion.

"Taken together, our findings imply that the charter schools in North Carolina are increasingly serving the interests of relatively able white students in racially imbalanced schools," according to the paper by two Duke professors and one PhD candidate.

The paper's findings are surprising as they question a major tenet of the charter school movement — that charters provide a necessary service, helping predominantly low-income, minority students who have been let down by traditional schools.

Instead of doing that, are charter schools encouraging segregation and providing a better education to white students? The paper studies the charter sector in North Carolina between 1999 and 2012 and has four main findings.

1. While charters in North Carolina started out serving disproportionately minority students, over time it has begun to serve more and more white students. In addition to an increasing number of white students being served at charter schools, charters are also becoming "more racially imbalanced," meaning that "some are serving primarily minority students and others are serving primarily white students."

As you can see, a smaller and smaller percentage of African-American students were enrolled. NBER Working Paper

2. Parents whose children attend charters with predominately white students are more satisfied with their schools than parents with children in predominantly minority charters. The researchers use the percentage of student turnover (kids who don't stay in the school the following year) as a proxy for parent satisfaction.

The paper's researchers argue this supports their theory that "this difference in apparent satisfaction is consistent with the view that many white parents are using the charter schools, at least in part, to avoid more racially diverse traditional public schools."

3. Charter schools in North Carolina have improved in quality over time and now perform better than traditional public schools (TPS). However, the researchers don't believe this is due to program quality at charter schools over TPS. They believe that it has to do with selection and types of students who move into charter schools.

4. Taken as a whole, these results lead the paper's researchers to believe that charter schools have becoming extremely segmented over time and increasingly serve the interests of white, middle-class families.

The researchers stop short of providing suggestions for improving this trend, but do call on policy makers to use their power and responsibility to influence the evolution of the charter sector in North Carolina.