Treatment fidelity as a predictor of behaviour change in parents attending group-based parent training C. Eames, D. Daley, J. Hutchings, C. J. Whitaker, K. Jones, J. C. Hughes and T. Bywater School of Psychology, College of Health and Behavioural Sciences, Bangor University, Gwynedd, UK Accepted for publication 8 February 2009 Keywords behaviour, fidelity, parenting, preschool children, treatment Correspondence: Catrin Eames BSc, School of Psychology, College of Health and Behavioural Sciences, Bangor University, Gwynedd LL57 2AS, UK E-mail: c.eames@bangor.ac.uk Abstract Background Change in parenting skills, particularly increased positive parenting, has been identified as the key component of successful evidence-based parent training (PT), playing a causal role in subsequent child behaviour change for both prevention and treatment of Conduct Disorder. The amount of change in parenting skills observed after PT varies and may be accounted for by both the content of the programme and by the level of PT implementer process skills. Such variation in implementer skills is an important component in the assessment of treatment fidelity, itself an essential factor in successful intervention outcome. Aims To establish whether the Leader Observation Tool, a reliable and valid process skills fidelity measure, can predict change in parenting skills after attendance on the Incredible Years PT programme. Results Positive leader skills categories of the Leader Observation Tool significantly predicted change in both parent-reported and independently observed parenting skills behaviour, which in turn, predicted change in child behaviour outcome. Conclusions Delivering an intervention with a high level of treatment fidelity not only preserves the behaviour change mechanisms of the intervention, but can also predict parental behaviour change, which itself predicts child behaviour change as a result of treatment. Introduction Conduct Disorder in the early years One in 10 of 5- to 16-year-olds in the UK has a mental health disorder meeting clinical criteria, with Conduct Disorder (CD) the most prevalent of these, accounting for 60% of children with mental health disorders (Office for National Statistics 2004). Disruptive behaviour problems among children aged five and over are the most common reason for mental health service referral in both the UK and the USA (Belsky et al. 2006). Externalizing behaviour patterns such as aggression towards peers, non-compliance and poor impulse regulation can be identified in early childhood and are precursors to clinically significant behaviour problems that become evident during school age and which, without intervention, can remain stable from toddler-hood throughout childhood, adolescence and adulthood (Richman et al. 1982; Campbell 1995; Pierce et al. 1999). Despite formal diagnosis predomi- nantly occurring between middle childhood and middle ado- lescence, it may also occur in the preschool years [American Psychiatric Association (APA) 2000], sometimes as early as 2 years of age (Shaw et al. 2000; Wakschlag and colleagues 2005). Child: care, health and development Original Article doi:10.1111/j.1365-2214.2009.00975.x © 2009 The Authors Journal compilation © 2009 Blackwell Publishing Ltd 603