Advocates of expanding the educational options available to students from low-income families raise not only social justice arguments—pointing to the choices made by families that can afford to live close to a good public school or pay private-school tuition—but also the theory that competition induced by expanded school choice will be “the proverbial rising tide that lifts all boats.” Breaking the ironclad link between residence and school attended will, proponents argue, force schools to compete for students and resources in ways that increase the quality of education provided.
But critics of school choice policies argue that these reforms will lead to increased segregation by race and class as more motivated families move to better schools, leaving the most disadvantaged students behind in the worst public schools. Criticism has often focused on charter schools given the growth in the charter sector in recent years. Nationwide, charter enrollment grew from 1 to 3 percent of all students between 1999-2000 and 2009-10. Charters make up a much larger share of the market in several places, including 11 percent of Arizona students and 37 percent in the District of Columbia.
Charter critics point to reports showing differences in the demographic characteristics of charter school students and their counterparts in traditional public schools as evidence that choice leads to segregation. For example, a 2010 report by UCLA’s Civil Rights Project found that black charter school students were twice as likely to attend schools that enrolled fewer than 10 percent non-minority students as their counterparts in traditional public schools. This type of analysis says little about segregation because it compares charter schools to all schools nationwide, when charter schools tend to be located in areas with large concentrations of minority students. A reanalysis of the data used in the UCLA report found much smaller differences between charter and traditional public schools once more appropriate comparisons were made between the two groups of schools.
But any comparison of the demographics of students in charter and traditional public schools provides at best an incomplete picture of segregation because segregation resulting from school choice policies would occur primarily across schools, not within schools. The existence of charter schools could alter the composition of traditional public schools (by drawing students away from them), thereby compromising comparisons between the two sectors as a source of information about the effect of choice on segregation. However, a RAND study found that, in most states, students tend to transfer between traditional public and charter schools with similar racial compositions.
I provide new evidence on this question based on an analysis of nine years of data from the Common Core of Data, the federal government’s annual census of all public schools. For each of the more than 3,000 counties in the U.S., I calculate an “exposure index” that measures the share of non-minority students at the schools attended by the average under-represented minority student. The average minority student in the U.S. attends a school that is 33 percent non-minority. In other words, the typical minority student attends a majority-minority school. Likewise, the typical student eligible for free or reduced-price lunch (a proxy for economic disadvantage) attends a school where almost two-thirds of students are also eligible for a subsidized lunch.
A naïve examination of the relationship between this measure of (de)segregation and the percentage of students enrolled in charter schools appears to show that the critics are right: more choice is associated with minority students attending less diverse schools. For the 2010-11 school year, a 10-percentage-point increase in charter enrollment is associated with a decline of 16 percentage points in minority students’ exposure to non-minority students. A similar but weaker relationship exists along class lines (as measured by free lunch eligibility).
Of course, this relationship ignores the fact that charters tend to locate in areas that serve large shares of disadvantaged students and members of minority groups. As a result, this simple correlation tells us nothing about whether charters increase segregation or just tend to locate in areas where the schools are already segregated. This is the same methodological flaw that compromised the findings of the UCLA study.
A better approach to the question of whether choice increases segregation is to look at changes over time. Did areas that saw large increases in choice experience larger increases in segregation than areas that saw smaller increases in choice? This kind of analysis does not conclusively measure the causal effect of choice on segregation, but by examining the same locales over time it represents a clear improvement over the cruder approach of comparing different locales at the same point in time. For example, it takes into account any unmeasured factors, such as the degree of residential segregation, to the extent that those factors remain constant over time.
Figure 1 shows the relationship between the change in charter enrollment and the change in minority exposure to non-minority students between 2002-03 and 2010-11. The cloud of points suggests little relationship between these two factors, and a regression analysis confirms that this is the case. There is actually a slight positive (and statistically significant) relationship between choice and diversity, but it is very weak and is not also found in the free-lunch data.
Figure 1. Change in Minority Exposure to Non-Minority Students vs. Change in Charter Enrollment, U.S. Counties, 2002-03 to 2010-11
I also used an alternative measure of segregation called a “dissimilarity index” and obtained similar findings: no consistent relationship between changes in charter enrollment and changes in segregation. Finally, I conducted a more sophisticated panel data analysis that uses all nine years of data to estimate the relationship between charter enrollment and segregation using only the changes within counties over time. Once again, using both the exposure and dissimilarity indices, the results consistently indicated no meaningful relationship between choice and segregation.
The lack of any consistent relationship between charter enrollment and segregation does not eliminate the possibility that such a relationship exists, but suggests that it is unlikely. For there to be a relationship, it would have to be the case that counties where charter enrollment increased experienced an increase in segregation as a result but then adopted policies (or experienced other changes) that counteracted the increase in segregation. In my view, that is not a very plausible explanation for these results.
There is no doubt that the high level of segregation in American society, including in our schools, is an important problem in its own right. The findings reported here indicate that it is unlikely that charter schools—a prominent effort to increase school choice, especially for students from disadvantaged backgrounds—are making the problem worse. But school choice policies come in a variety of flavors which may have different effects on the demographic makeup of schools. There may be examples of poorly designed choice programs that have increased segregation. For example, a choice system that is complicated and difficult to navigate may advantage affluent, educated parents at the expense of other parents.
Conversely, perhaps carefully designed choice policies can play a role in lessening the segregation of schools by race and class. For example, a simple, streamlined process that allows families to choose any school in a large urban district—and uses a fair method for allocating spaces at oversubscribed schools—could be a way to weaken the link between residential and school segregation that has plagued our school system since the end of legally mandated segregation more than 50 years ago.
 Of course students can also be segregated within schools, such as through the classrooms to which they are assigned or courses they decide to take, but that type of segregation is not usually the focus of critics of school choice policies.
 I define under-represented minority to include American Indian, black, and Hispanic students.
 The average county experienced an increase of charter enrollment of 1 percentage point, with a standard deviation of 4 percentage points. Weighted by student enrollment, the average increase is 2 percentage points with a standard deviation of 4 percentage points.
 The regression analysis and line in Figure 1 are both weighted by the number of minority students in each county (using the average of 2002-03 and 2010-11)
 This analysis pooled data from all years and included both year and county fixed effects.