Why target early adolescents and parents in alcohol prevention? The mediating effects of self-control, rules and attitudes about alcohol use Ina M. Koning 1,2 , Regina J. J. M. van den Eijnden 1 , Rutger C. M. E. Engels 3 , Jacqueline E. E. Verdurmen 2 & Wilma A. M. Vollebergh 1 Department of Interdisciplinary Social Science, Utrecht University, Utrecht, the Netherlands, 1 Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands 2 and Institute of Family and Child Care Studies, Radboud University Nijmegen, Nijmegen, the Netherlands 3 ABSTRACT 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. Keywords Alcohol use, early adolescents, intervention, mediation, randomized trial. Correspondence to: Ina M. Koning, Interdisciplinary Social Science, Utrecht University, PO Box 80.140, 3508TC Utrecht, the Netherlands. E-mail: i.koning@uu.nl Submitted 2 December 2009; initial review completed 18 February 2010; final version accepted 9 September 2010 INTRODUCTION Given the risks involved in drinking alcohol at an early age [1], researchers, prevention workers and parents question how they can prevent early adolescents from starting to drink alcohol. A potentially effective strategy for delaying the onset of drinking is to carry out alcohol prevention programmes in which adolescents, as well as their parents, are targeted. Reviews on the effectiveness of alcohol interventions show preventive interventions for young adolescents to be most effective when both adoles- cents and their parents are targeted simultaneously [2,3]. In agreement with this finding, a recent study demon- strated that a Dutch prevention programme was effective in delaying the onset of weekly drinking, especially when adolescents and their parents were targeted simulta- neously, whereas targeting adolescents or their parents separately revealed no effects [4]. In extension to this finding, it is imperative to understand the effect of the interventions on the putative mediators and to analyse how such an alcohol intervention achieves its impact. Insight into through which processes an intervention achieves its effects is generated usually by detecting factors that are changed by the intervention and that RESEARCH REPORT doi:10.1111/j.1360-0443.2010.03198.x © 2010 The Authors, Addiction © 2010 Society for the Study of Addiction Addiction, 106, 538–546