Introduction The effect of socioeconomic status on adolescent substance abuse may be mediated by family socialization practices. However, traditional mediation analysis using a product or difference method is susceptible to bias when assumptions are not addressed. We aimed to use a potential outcomes framework to assess assumptions of exposure-mediator interaction and of no confounding of the results. Method We revisited a traditional mediation analysis with a multiple mediator causal mediation approach using data from 17,761 Norwegian young people (13–18 years), 51% female. Data were collected through a print questionnaire. Socioeconomic status was operationalized as parental education and employment status (employed or receiving welfare); drinking behavior as the frequency of alcohol consumption and frequency of intoxication in the past year; and socialization practices as general parenting measures, alcohol-related parental permissiveness, and parent drinking behavior. Results There was no consistent evidence of exposure-mediator interaction. Formal sensitivity analysis of mediator-outcome confounding was not possible in the multiple mediator model, and this analysis supported the hypothesis that socioeconomic status effects on adolescent substance abuse are fully mediated by family socialization practices, with apparently stronger effects in younger age groups observed in plots. Conclusion We found that the effect of socioeconomic status on adolescent substance abuse was fully mediated by family socialization practices. While our analysis provides more rigorous support for causal inferences than past work, we could not completely rule out the possibility of unmeasured confounding.