The study—which was authored by Edward Morris, a sociologist at the University of Kentucky, and Brea Perry, a sociologist at Indiana University—concludes that school suspensions account for roughly one-fifth of the white-black achievement gap. “Particularly for African American students in our data, the unequal suspension rate is one of the most important factors hindering academic progress and maintaining the racial gap in achievement,” Morris and Berry write, describing discipline patterns as an example of “hidden inequality embedded within routine educational practices.” During the 2011-12 school year, black children accounted for 16 percent of the U.S. student population but 32 percent of the students suspended and 42 percent of those expelled, according to Education Department data; nationwide, black students are suspended at roughly three times the rate as their white counterparts.

Suspensions and expulsions take a toll on student achievement in various ways, some of them obvious. For one, they take students out of school, which can easily hinder their academic progress. For another, they often weaken school bonds, disengaging children from their teachers and learning. Other research, also by Morris and Perry, has suggested that high suspension rates can undermine student achievement as a whole, even for children who weren’t personally suspended.

Still, little empirical evidence exists to demonstrate a direct link between suspensions and achievement—to show that the suspensions themselves are responsible for lower performance. While Morris and Perry’s latest study can’t prove that there’s a causal relationship between suspension and achievement, it does use longitudinal data to show a strong connection between the unequal suspension rates and the persistence of the race-based achievement gap.

The researchers studied a sample of a little over 16,000 male and female middle- and high-schoolers at 17 campuses in Kentucky over a three-year period beginning in 2008. Most of the students included (59 percent) were white, while 25 percent were black and 10 percent were Latino. While the focus on Kentucky means the sample isn’t nationally representative, Morris and Perry argue that it’s “reasonably representative” of the Southeastern U.S., a region where exclusionary discipline is especially common.

The researchers found that, even within a single school, black students were six times as likely to be suspended as white students. One could argue the likelihood a child is disciplined in school depends more on things like income and family structure than it does on race. And in some cases, it does: The elevated rates of discipline among Latino students included in Morris and Perry’s study, for example, are “entirely explained by this group’s lower levels of socioeconomic status.” However, even after controlling for income—as well as other relevant factors, including gender and participation in special education—black students were suspended at three times the rate as their white peers, suggesting that race itself plays an important role in the discipline rates. Separate research, meanwhile, has found racial discrepancies in how discipline is administered, including for similar offenses.