There is a large body of evidence revealing that minorities--in particular, Black citizens--are overrepresented in the criminal justice system. But the causes of these inequalities have been difficult to pin down. One line of work suggests the inequalities in arrest may be traced to inequalities in exposure to school discipline. Specifically, the school-to-prison pipeline literature suggests inequalities in school disciplinary practices may go on to produce inequalities in arrest prevalence. In this article, we draw on a large nationally representative sample to test the hypothesis that racial inequalities in school-based punishments will (partially) explain inequalities in adulthood arrest. We find support for this pathway and, by drawing on recent developments in epidemiology, produce initial estimates of the degree to which policymakers might be able to close the racial gap in arrest if it were possible to close the racial gap in school discipline.