Some children have challenging behaviour that lasts beyond the ‘terrible twos’ and begins to have serious consequences, with difficulties that continue into adulthood. Parent-Child Interaction Therapy (PCIT) is a unique training programme for parents of young children with conduct problems. Parents wear an earpiece and interact with their child in a specific way while being coached by a highly trained clinician who provides live support and immediate feedback from behind a one-way mirror. This project aims to explore the effectiveness of the existing intervention in the ‘real world’ of NZ child mental health services, by looking at data from families who have completed the programme, and to explore how more families in need can be offered the intervention. A small investment in young children with challenging behaviour can pay significant dividends in later years - for the child, their family, and for society.