School segregation has proven to be one of America’s most intractable problems—difficult to change and complicated to understand.
Traditionally, we talk about segregation by looking at a school’s racial or ethnic makeup. Do Black or Hispanic students learn alongside many white students at their school? If not, it’s typically considered segregated.
But this approach misses that all-white schools are just as segregated as all-Black or all-Hispanic schools and that segregation is about more than just the race or ethnicity of students at a particular school. It’s also about the racial and ethnic demographics of a school’s community and the distribution of students across schools in that system.
As the US becomes more racially diverse, we need measures of segregation that help education leaders develop solutions that will have the biggest impact. By better understanding school segregation, we can find better ways to address it.
That’s why we created the Segregation Contribution Index (SCI), which measures how much individual schools contribute to racial segregation in their broader systems.
Take, for instance, Tamarack Waldorf School in Milwaukee, Wisconsin, a PK–8 private school where 36 percent of its middle school students are Black or Hispanic.i We argue that desegregation efforts should focus on inequities in student achievement. Evidence shows that, on average, structural factors have led Black and Hispanic students to persistently score lower in standardized examinations than white and Asian students. Thus, we measure school segregation as the separation of Black and Hispanic students from white and Asian students (and the relatively small share of students from other racial or ethnic groups). We recognize the limitations of this grouping, as these students have different experiences in education systems.
Using common measures of segregation, which often define schools as intensely segregated if less than 10 percent of enrolled students are white, Tamarack wouldn’t be considered particularly segregated.
But that approach doesn’t consider the racial composition of the school’s district.i We group schools into geographic school district boundaries, which is important for linking charter and private schools to school districts because they don’t use the same administrative identifiers as traditional public schools. Compared with the Milwaukee school district, in which the Black or Hispanic enrollment share among middle school students is 80 percent, Tamarack has a much smaller share of Black or Hispanic students.
We can look at all 172 schools serving middle school students in the Milwaukee school district to see how their racial composition compares with district-wide enrollment. Tamarack is on the far left of this distribution, which means it enrolls a smaller share of Black or Hispanic middle school students than most schools.
To determine whether a school is segregated, rather than looking only at its share of Black or Hispanic students, we can consider how changing that share would affect integration in the district. Derived from the dissimilarity index, our SCI assigns each school a percentage showing how much segregation in the district would fall if that school’s racial composition matched the district’s.
If all schools in a district were the same size, their SCI percentages would directly correlate to how much smaller or larger their shares of Black or Hispanic students are than the district’s share.
But size is also a factor, because changing a larger school’s racial composition affects a bigger share of the district’s students. To calculate each school’s SCI value, we account for the difference in the share of Black or Hispanic students between the school and its district, as well as the school’s total enrollment. The SCI percentage reflects the share of district-wide segregation that can be attributed to the individual school.
In this case, Tamarack has an SCI value of 0.77 percent. That means if the school’s racial composition matched the composition of the Milwaukee School District’s middle school enrollment, segregation in the district would fall 0.77 percent. Tamarack enrolls 72 middle school students. If it were bigger, it would contribute even more to district segregation because changing the school’s racial composition would involve more students.
So how does this change how we typically think about school segregation?
Traditional measures of segregation that look only at a school’s racial composition may miss schools that look vastly different from their districts, and these measures don’t quantify how much each school contributes to broader system segregation.
Our measure treats schools as parts of a whole: each school contributes a certain share to total segregation in the broader system.
Beyond that, our SCI shifts conventional thinking about which schools are considered segregated. Absolute measures of segregation are often based on whether schools enroll large shares of Black or Hispanic students.
But using our new measure, we see that many schools with a smaller share of Black or Hispanic students than the district contribute just as much—or even more—to segregation as schools with a larger share of Black or Hispanic students.
In the Milwaukee school district, 52 of the 172 middle schools have a smaller share of Black or Hispanic students than the district. Even though these schools enroll only 33 percent of all district middle school students, they account for 50 percent of the district’s segregation.
Of course, neighborhoods are often severely racially segregated, which drives a large part of school segregation patterns. But residential segregation doesn’t explain everything. In many cases, the racial composition of students who attend schools in the area around a given school is vastly different from that school’s enrollment. Among the five schools within one mile of Tamarack (including Tamarack), 89 percent of middle school students are Black or Hispanic.
That difference shows that transportation isn’t the only barrier for integration efforts. School attendance boundaries, as well as other factors like tuition, entrance exams, school choice policies, and parent preferences also contribute to segregation.
To drive greater change, local policymakers concerned about segregation can use this improved measure to target desegregation efforts at schools where changes would have the biggest impact on the district, and to identify structural factors that may impede integration.