Controlled trials demonstrate that parenting programs work, but less is known about the processes of change, contextual factors or intervention characteristics that influence trial outcomes. This qualitative study assessed the experiences of Irish parents involved in a randomized controlled trial of the Incredible Years BASIC parenting program, with a view to understanding how and why the program works, or does not work, within disadvantaged settings. Data from 33 parents of young children (aged 3–7 years) with conduct problems were collected by semi-structured interviews and analysed using constructivist grounded theory. Emerging themes indicated that parents perceived the program to have produced positive changes through learning key parenting skills (e.g. positive attention, empathy and problem-solving skills) and through enhanced parental mood/confidence, derived primarily from gaining non-judgmental support from the group. Parents also experienced cultural, personal and environmental challenges in learning the new skills, including discomfort with praise and positive attention, conflict with their partner and parenting within an antisocial environment. Parents dropped out of the course for largely circumstantial reasons. These findings should help to inform the future implementation of this well-known parenting program both in Ireland and elsewhere.