The movement from middle school to high school is a normative transition that is typically associated with increased stress and opportunity in social and academic domains. Theoretically, this transition may reflect a turning point in terms of initiating or sharply increasing heavy alcohol use, a notion that has received little attention in the empirical literature. The present study draws on a nationally representative data set, the National Longitudinal Survey of Youth 1997 (NLSY97), to examine the impact of the high-school transition on increases in alcohol use. The multiwave multicohort design of NLSY97 permits explicit coding of the high-school transition for 3,360 adolescents (48% female; 54% non-Black/non-Hispanic). Using latent transition analysis, we examined transitions among nondrinking, light drinking, and heavy drinking classes to characterize initiation of use and progression to heavier drinking. Non-Black/non-Hispanic youth and those higher on delinquent behaviors were more likely to be involved in alcohol prior to the transition and more likely to rapidly escalate their use with the transition. Although no sex differences were observed prior to the high-school transition, girls were more likely to transition from nondrinking to light drinking, whereas boys were more likely to transition to heavy drinking. High monitoring was associated with greater progression from light drinking in middle school to heavy drinking in high school; low and moderate parental monitoring were associated with initiation of heavy drinking across the transition. The high-school transition is a time of increased risk for many young people, and greater attention to this important school transition as a time to intervene is warranted.