Prior research has found a strong relationship between substance use and beliefs about normative behavior. In understanding the influence of initial levels and change over time in adolescent normative beliefs on longitudinal substance initiation, a study of growth trajectories was recommended. The goal of this study was two-fold. First, it investigated individual differences in the initial levels and growth-trajectories of normative beliefs and substance initiation, and second, examined a longitudinal model in which baseline levels of academic achievement influenced both initial levels and growth-trajectories of normative beliefs and substance initiation. Specifically, the study investigated the effects of baseline levels of academic achievement and longitudinal trends in normative beliefs on adolescent substance initiation across a 42-month time period. The study consisted of 272 seventh grade students from rural counties in a Midwestern State. Five assessments were conducted. Results from the study indicate that academic achievement positively predicted the intercept and negatively predicted the growth-trajectory of normative beliefs regarding peer substance behavior. In addition, baseline academic achievement negatively predicted initial levels, as well as the growth trajectory of substance initiation. Overall, the investigation stimulated questions for further research in the investigation of pathways between the study constructs. Tables, references and appendix