This study reviewed 177 primary prevention programs that were designed to prevent behavioral and social problems in children and adolescents.  The authors find that, on average, a participant in a primary prevention program surpasses the performance of between 59% to 82% of those in a control group.  In addition, the outcomes reflect an 8% to 46% difference in success rates favoring prevention groups.

Durlak, J. A. and Wells, A. M. (1998). Primary prevention mental health programs for children and adolescents: a meta-analytic review. American Journal of Community Psychology, 25(2): 115-152. DOI: 10.1023/A:1024654026646 http://www.springerlink.com/content/m2017505825t7l70/

Authors: Joseph A. Durlak, Anne M. Wells