The typical pattern for intervention outcome studies for conduct problems has been for effect sizes to dissipate over time with decreasing effects across subsequent follow-ups.

To establish whether the short-term positive effects of a parenting programme are sustained longer term. To observe trends, and costs, in health and social service use after intervention.

Parents with children aged 36–59 months at risk of developing conduct disorder (n = 104) received intervention between baseline and first follow-up (6 months after baseline n = 86) in 11 Sure Start areas in North Wales. Follow-ups two (n = 82) and three (n = 79) occurred 12 and 18 months after baseline. Child problem behaviour and parenting skills were assessed via parent self-report and direct observation in the home.

The significant parent-reported improvements in primary measures of child behaviour, parent behaviour, parental stress and depression gained at follow-up one were maintained to follow-up three, as were improved observed child and parent behaviours. Overall, 63% of children made a minimum significant change (0.3 standard deviations) on the Eyberg Child Behavior Inventory problem scale between baseline and follow-up (using intention-to-treat data), 54% made a large change (0.8 standard deviations) and 39% made a very large change (1.5 standard deviations). Child contact with health and social services had reduced at follow-up three.

Early parent-based intervention reduced child antisocial behaviour and benefits were maintained, with reduced reliance on health and social service provision, over time.