This is possible because many measures of school segregation are narrow, focusing only on a single symptom. For instance, one common research technique is to count the number of schools above a certain demographic cutoff (for instance, more than 90 percent nonwhite). Another is to focus on “exposure,” or how common it is for white and nonwhite students to encounter each other in the education system.

Doubters like VerBruggen argue that people using these metrics have been fooled by demographic change. The past several decades have seen a precipitous increase in the racial diversity of U.S. schoolchildren. For example, since 1996, the share of Hispanic and Asian students in public schools has grown from 17 to 31 percent. As a result, across the board, schools have tended to become less white.

When diversity increases, some measures of segregation are likely to get worse, more or less by default. For instance, if an integrated school is growing, but most of the new students are Hispanic, at some point, it’ll tip over and become segregated. If white students become a smaller share of the American population overall, all else equal, “exposure” to white students will probably decline.

VerBruggen claims that this shift, and little else, is responsible for the perceived crisis. “The rise in ‘segregation’ disappears when one measures segregation properly,” he asserts. He and others say that, with slim evidence of increasing segregation, policies designed to proactively integrate schools are an obsolete form of social engineering.

It’s a simple case. Too simple: There is plenty of evidence that resegregation is urgently real.

School segregation seems like it would be easy to gauge: Just add up the number of segregated schools, and see whether that number is going up or down over time. But the reality, unfortunately, is a lot more complicated.

The core problem is that the nation’s schools are evolving in many ways at once. Student populations undergo slow shifts; new schools are constantly opening and closing; attendance boundaries are drawn and redrawn. As a result, the effects of large-scale demographic change and those of local school policy get tangled up with one another. It can be hard for researchers to separate one factor from the other.

Making things even tougher, increased national diversity tends to generate mixed signals about whether segregation is happening. As skeptics like Verbruggen point out, some measures of segregation, especially those that focus on the prevalence of white students, tend to look worse when student diversity increases. But other measures tend to look better. For example, one statistic known as a “dissimilarity index” calculates how many people would have to swap places to achieve demographic balance. When diversity increases evenly, dissimilarity indexes will improve—because the share of minority students in the least-integrated schools will grow, making fewer swaps necessary.