Background Early risk factors for poor child outcomes are well established, and some group parenting programmes have demonstrated good outcomes for children under 3 years of age. This randomized controlled trial evaluated the effectiveness of the Incredible Years® Toddler Parenting Programme with parents of 1‐year‐old and 2‐year‐old children recruited by staff in disadvantaged Flying Start areas across Wales. Methods Eighty‐nine families with a child aged between 12 and 36 months at baseline participated in a pragmatic community‐based trial of the programme in eight Flying Start areas. Outcomes were measured at baseline, 6 months and 12 months using measures of parental mental health, competence, child behaviour, child development, home environment and blinded‐observation of parent–child interactions. Results Significant intervention group improvements were found in parental mental well‐being and observed praise at 6 months. Significant improvements for the intervention group at 12 months included child development, home environment and parental depression. Conclusion The study provides preliminary evidence for programme attendance.