“The Growing Segmentation of the Charter School Sector in North Carolina” is a new National Bureau of Economic Research (NBER) paper written by Helen Ladd, Charles Clotfelter, and John Holbein of Duke University.  They conclude,

…we document that the charter schools as a group initially started out behind the traditional public schools in terms of the test score gains of their students. Over time, however, the distributions across schools in the two sectors converged and now charter school students tend to have higher test score gains than those attending the traditional public schools. This finding reflects in part the winnowing out of charter schools whose students performed poorly, and, in recent years, the entry of schools whose students performed better, a process that is consistent with predictions that market forces would drive under-performing schools out of business. The apparent success of the charter schools entering after 2006 has likely been enhanced by a policy change in that year that required charter schools to delay opening for a year after their charter was approved, and the associated support provided by the state’s Office of Charter Schools during and after that year.

The authors contend that the “changing clientele of charter schools” is another possible explanation for the superior performance of charter schools.  That is a nice way of saying that charter schools are reaping the benefits of “white flight” and becoming more segregated.  I suspect closure, quality control, and clientele have all played a role in raising student achievement in charters.

I question their use of free/reduced lunch status.  Charter schools that do not participate in the federal School Lunch Program have no free/reduced lunch students. But these schools still enroll students who are economically disadvantaged.

I also disagree with some of their conclusions.  For example, they argue that “many white parents are using the charter schools, at least in part, to avoid more racially diverse traditional public schools” because white parents report higher rates of satisfaction with their choice, compared to those whose children are in predominantly minority charter schools.  The authors admit that there is no way to confirm this, but it sure goes well with their thesis.