To evaluate the net effects of classroom disciplinary practices, policy makers and educators must understand not only their effects on disciplined students but also their effects on non-disciplined peers. In this study, we estimate the link between peer suspensions and non-suspended students’ learning trajectories in a California school district where middle and high school students took up to twelve basic skills tests in mathematics and English Language Arts (ELA) over the course of the 2009–10, 2010–11, and 2011–12 school years. We find that Hispanic students, students eligible for free or reduced-price lunch, English language learners, students enrolled in special education, and low-achieving students are disproportionately exposed to classmate suspensions. Analyses with student and classroom fixed effects show that student achievement in mathematics increases when their classmates receive suspensions, particularly suspensions attributed to disruptive behavior. We find no association between classmate suspension and ELA achievement. Because these results come from schools in which suspensions are relatively rare events, they may not generalize to settings with draconian disciplinary cultures. Nonetheless, our findings imply that suspensions, when used appropriately, can improve the academic achievement of non-suspended students, particularly for students from vulnerable populations.