Aims To examine the effects of a parent and student intervention offered separately and simultaneously (PAS) on onset of weekly drinking via its putative mediators.
Design A randomized trial with four conditions; (1) parent intervention, (2) student intervention, (3) combined parent–student intervention and (4) control group.
Setting High schools selected randomly, located in different areas.
Participants A total of 2937 early adolescents (mean age = 12.6, standard deviation = 0.49) and their parents.
Measurements Mediation effects were analysed using pretest data and two follow-up measurements (10 and 22 months after baseline). A path model was estimated (Mplus) to examine the effect of the interventions on adolescent-reported mediators (self-control, perceived parental rules and attitudes about alcohol) and parent-reported mediators (parental rules and attitudes about alcohol). Outcome was onset of weekly drinking.
Findings The parent intervention modified rules and attitudes about alcohol as reported by parents. An indirect effect of the parent intervention via parental rules was found. The combined intervention affected both adolescent-reported and parent-reported rules and attitudes about alcohol and adolescents' perceived self-control, yet only perceived rules and self-efficacy, as reported by adolescents, and parental attitudes mediated the association between the combined intervention and onset of weekly drinking. No significant effects were found of the separate student intervention on the mediating factors.
Conclusions The PAS programme proved to be effective as predicted by the theoretical assumptions underlying the interventions. Interventions with parents and adolescents to prevent adolescent alcohol consumption may usefully target parental rules about alcohol and adolescents' self-confidence.