Black youth are disproportionately exposed to school exclusionary discipline. We examined the impact of race on age at the onset of school disciplinary actions and police contact, and the rate of receiving increasingly severe disciplinary actions. Youth (N= 2,156) and their caregivers participating in the Adolescent Brain Cognitive Development Social Development (ABCD-SD) study reported on the occurrence and timing of disciplinary events and youths' demographics, delinquency, and neighborhood conditions. Experiences of exclusionary discipline were analyzed using logistic regression and Cox proportional hazards models. Black youth reported significantly higher rates of almost all disciplinary events compared to White youth. In logistic regression and Cox models, Black youth experienced higher risk for exclusionary discipline and police contact (odds ratios from 2.47 [detention] to 5.16 [sent home]; hazard ratios from 1.36 [detention] to 4.71 [expelled]), even after adjusting for sex, delinquency, neighborhood conditions, and the interaction between race and sex. Black youth who received detention and suspension were at higher risk for additional, more severe school discipline than were White youth. Consistent with a racial bias in exclusionary discipline practices and policing, Black youth, particularly Black male youth, were at a higher risk for experiencing almost all disciplinary outcomes and at younger ages than White youth, after controlling for delinquency, sex, and neighborhood factors. Compared to White students, school detention and suspension status predicted an accelerated cascade of school discipline outcomes for Black students, suggesting racial disparities in how the severity of school discipline escalates over time. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science. We actively worked to promote inclusion of historically underrepresented racial and/or ethnic groups in science in our author group. While citing references scientifically relevant for this work, we also actively worked to promote sex and gender balance in our reference list. While citing references scientifically relevant for this work, we also actively worked to promote inclusion of historically underrepresented racial and/or ethnic groups in science in our reference list.