This paper identifies key themes from research into programme fidelity of sexual abuse prevention programmes. It presents a detailed analysis of programme fidelity within a study of the Tweenees school-based abuse prevention programme (Barron and Topping, 2010). The paper reports how programme fidelity was addressed in a programme delivered to survivors of child sexual abuse by experienced survivor organisation workers. There was also study of programme fidelity in the delivery of the programme to grade-seven pupils through co-working between survivor organisation workers and teachers. Video was taken of all four sessions delivered to the survivors' group. To begin to explore programme fidelity when lessons were co-delivered by survivor organisation workers and a teacher, the first session of a grade-seven class was videoed. Survivor organisation workers achieved high levels of programme fidelity characterised by facilitative communicative behaviours (e.g. affirming responses, seeking clarification, checking understanding and summarising). The grade-seven teacher's communication was characterised by a behaviour management focus. Video analysis of interactions was a useful measure for programme fidelity and analysing appropriate communication underpinning delivery of the programme. Recommendations for future programme fidelity measures are provided for researchers and practitioners in the field. Copyright © 2010 John Wiley & Sons, Ltd.