A recent paper touting gains in Kentucky’s Focus schools (schools with the lowest performance for student groups) is, on the surface, encouraging. We want to know more about what’s driving these gains. But we’re also worried about assertions made by the authors, who suggest that these improvements could be attributed to the use of a “supergroup” — which combines students from low-income families, English learners, students with disabilities, and students of color into one umbrella group — in the state’s accountability system.

It’s important to note that this claim is just the authors’ theory; it is unsubstantiated by the study itself. The actual study doesn’t look at, much less prove, that a supergroup measure — rather than some other feature of Kentucky’s school accountability system — is the reason we see these improvements. And that’s particularly misleading in times like these, when states are actively working on developing accountability and improvement systems under the Every Student Succeeds Act.

The problem with supergroups is that, by combining multiple historically underserved groups of students together, they allow the results of one group to overshadow those of another and enable schools to hide their underperformance for some student groups. Indeed, we see this in the NBER paper itself. The study looked only at the results for the supergroup, which in Kentucky are driven mostly by the results of White, low-income students. So while the paper reports that in Focus schools, supergroup math proficiency rates increased by 5 percentage points and reading rates by 3.5 percentage points in one school year, it does not tell us how much schools improved for students of color, students with disabilities, or English learners.

As the NBER paper suggests, states, like Kentucky, can — and should — take a more active role in supporting school improvement. Kentucky, for example, required its schools that were especially low performing for the supergroup to conduct a needs assessment and submit a comprehensive school improvement plan for review; and then it provided a set of recommended initiatives. But despite the authors’ suggestion that the use of the supergroup contributed to the schools’ improvement, the study does not actually show any benefits of ignoring meaningful distinctions between the needs of — and civil rights protections afforded to — each group of children by lumping them together in a supergroup.