Childhood adversity can have detrimental impacts on life course mental and physical health. Timing, nature, severity, and chronicity of adversity are thought to explain much of the variability in health and developmental outcomes among exposed individuals. The current study seeks to characterize heterogeneity in adverse experiences over time at the individual, family, and neighborhood domains in a cohort of predominantly Black children (85% Black and 15% White, 46.2% girls, 67.2% free/reduced lunch in first grade), and to examine associations with mental health from sixth grade to age 26. Participants were part of a randomized universal preventive interventions trial in first grade with prospective follow-up through early adulthood. Separate models characterized heterogeneity in adversity in elementary, middle, and high schools. Changes in adversity over time and relationships with mental health (anxiety, depression, suicidal behaviors) were investigated using a random-intercept latent transition analysis (RI-LTA). We identified three-class solutions in early childhood, middle school, and high school. Generally, both a higher and a lower poly-adversity class were observed at each time point, with varying nature of adversity characterized by the third class. RI-LTA indicated prevalent within-individual changes in adverse exposure over time and differential associations with mental health and suicidal behaviors. Results suggest that treating adverse exposures as a static construct may limit the ability to characterize salientvariation over time. Identifying complexity in adverse experiences and their relation to health and well-being is key for developing and implementing effective prevention and early intervention efforts to mitigate negative effects through the life course.