Nationally, educators suspend Black students at greater rates than any other group. This disproportionality is fueled by stereotypes casting Black students as "troublemakers"--a label students too often internalize as part of their identities. Across two independent double-blind randomized field trials involving over 2,000 seventh graders in 11 middle schools, we tested the efficacy of a brief intervention to buffer students from stereotypes and mitigate the racial suspension gap. The self-affirmation intervention helps students access positive aspects of their identities less associated with troublemaking in school. Confirmed in both trials, treatment effects cut Black-White suspension and office disciplinary referral gaps during seventh and eighth grade by approximately two thirds, with even greater impacts for Black students with prior infractions.