Inappropriate parenting behavior in the family can be one of many risk factors in children's social development. Accordingly, prevention programs aim at improving parenting. The relation between parenting and problem behavior was investigated and an evaluation reported of parent training in the German prevention program EFFEKT (Entwicklungsförderung in Familien: Eltern- und Kinder-Training - Enhancing the development of families: parent and child training). As part of the Erlangen-Nuremberg Development and Prevention Study [Lösel, F., Beelmann, A., Jaursch, S., Koglin, U., Stemmler, M., 2005a. Entwicklung und Prävention früher Problem des Sozialverhaltens: Die Erlangen-Nürnberger Studie. In: Cierpka, M. (Ed.), Möglichkeiten der Gewaltprävention. Vandenhoeck und Ruprecht, Göttingen, pp. 201-249.], this paper presents data on 128 mothers and 16 fathers who participated in the parent training. The trained parents were compared with a matched control group on scales of self-reported parenting behavior. Significant effects were found 2-3 months after training and in a follow-up survey 1 year later. Trained mothers showed more positive parenting and less inconsistent discipline than control mothers. Results for fathers were not significant. Our results suggest that with the EFFEKT parent training it is possible to change the child's family environment in a positive manner, with relatively low costs for the parents regarding time and money, but with sustainable effects.