Who Benefits and How Does It Work? Moderators and Mediators of Outcome in an Effectiveness Trial of a Parenting Intervention Frances Gardner Department of Social Policy and Social Work, University of Oxford Judy Hutchings, Tracey Bywater, and Chris Whitaker Department of Psychology, Bangor University We examined mediators and moderators of change in conduct problems, in a multiagency randomized trial of the Incredible Years parenting program. Preschoolers (n ¼ 153) at risk for conduct problems were randomly assigned to intervention (n ¼ 104) and wait-list (n ¼ 49) groups. Boys and younger children, and those with more depressed mothers, tended to show greater improvement in conduct problems post-intervention. Other risk factors (i.e., teen or single parenthood, very low income, high initial levels of problem behavior) showed no predictive effects, implying intervention was at least as successful at helping the most disadvantaged families, compared to more advantaged. Mediator analyses found change in positive parenting skill predicted change in conduct problems. There are many parenting interventions for reducing child problem behavior that have been found to be efficacious in randomized controlled trials. Mostly these interventions have been tested in ‘‘efficacy’’ trials, under the relatively ideal conditions of a specialist or research clinic. Recently, because of the importance of informing prevention policy, there has been increasing interest in testing these programs in ‘‘effectiveness’’ trials in real- world settings (Weisz, Sandler, Durlak, & Anton, 2005), including mental health (Scott, Spender, Doolan, Jacobs, & Aspland, 2001), primary care (Turner & Sanders, 2006), schools (Dishion, Nelson, & Kavanagh, 2003), and welfare (Gardner, Shaw, Dishion, Burton, & Supplee, 2007) settings, and in the non-profit sector (Gardner, Burton, & Klimes, 2006) and in community settings for disadvantaged preschoolers (Hutchings, Bywater, Daley, Gardner et al., 2007; Webster-Stratton, 1998). These studies are essential for answering policy questions about whether parenting programs can be rolled out into regular, accessible services. They show that it is possible to deliver effective programs in com- munity settings to high-risk children. However, despite this large number of trials, relatively few so far have tested effectiveness of programs delivered by regular service staff (Weisz et al., 2005). Trials are not only useful for testing questions about effectiveness. They are also important for understanding which families benefit from intervention when they are rolled out more widely, and what are the critical ingredi- ents that contribute to success under real-world con- ditions (Weersing & Weisz, 2002). This article explores moderators and mediators of intervention effects within a randomized controlled trial of the Webster-Stratton (1998) ‘‘Incredible Years’’ parenting intervention aimed at preventing conduct problems in high risk preschool children. The trial took place within multiple ‘‘Sure Start’’ services, whose overall goal is to provide support services to communities with high proportions of low-income families. This study represents a true ‘‘effec- tiveness’’ trial by testing implementation of an We thank the families and staff who participated and the Health Foundation (Grant 1583=1566) for support. Correspondence should be addressed to Frances Gardner, Department of Social Policy & Social Work, University of Oxford, 32, Wellington Square, Oxford OX1 2ER, United Kingdom. E-mail: frances.gardner@socres.ox.ac.uk Journal of Clinical Child & Adolescent Psychology, 39(4), 568–580, 2010 Copyright # Taylor & Francis Group, LLC ISSN: 1537-4416 print=1537-4424 online DOI: 10.1080/15374416.2010.486315