This study extends previous research investigating the developmental pathways predicting adolescent alcohol and marijuana use by examining the cascading effects of externalizing and internalizing symptoms and academic competence in the prediction of use and level of use of these substances in adolescence. Participants (N = 191) were drawn from a longitudinal study of first-born children of low-income mothers. Using data from ages 7, 9, 12, and 16 years, a series of nested two-part (semi-continuous) path models from a developmental cascade modeling framework were compared. Controlling for gender, SES, mother's age at child's birth, and minority status, we found (a) within-domain rank-order stability across time, (b) significant cross-domain effects over time, (c) higher externalizing symptoms significantly predicted use of alcohol and marijuana as well as higher levels of use in adolescence, and (d) higher levels of academic competence significantly added to the prediction of use of alcohol. (Contains 6 tables and 2 figures.)