Modern evaluations of parent training programmes seek evidence not only of efficacy in optimal, often university clinic settings, but also of effectiveness under normal field conditions. The Kompetenztraining fur Eltern sozial auffalliger Kinder (KES) is a cognitive-behavioural competence training for parents of socially disruptive children. This study tried to complement the investigation of its efficacy by exploring its effectiveness under field conditions. Staff at 14 child guidance centres conducted the training with 88 parents (63.6% mothers; mean age 37.2 years). Effectiveness was assessed by comparing problem behaviour in the child and stress in the family (German versions of Home Situations Questionnaire and Parenting Stress Index) before and after training. Results showed mild to moderate declines in child behaviour problems and moodiness, as well as doubts in the parent role, and stronger effects in more versus less stressed families. Qualitative feedback from the trainers after running the programme was positive. It is concluded that the KES is a sufficiently promising parent training to justify further and more rigorous investigation under field conditions. (Contains 3 tables.)