Objective: To assess an intervention to familiarise parents with children's books for use in primary (5-11 years) sex and relationship education (SRE) classes. Method: Case study of a 7-week programme in one London primary school, using ethnographic observation, semi-structured interviews and focus groups with parents (n = 7) and key stakeholders (n = 4), and pre- and post-programme self-completion questionnaires (n = 9). Results: Parents reported increased understanding of the SRE curriculum and awareness of relevant children's books, enhanced interactions with their children on SRE topics and some positive effects on partners and attitudes towards the school. There was increased confidence in addressing issues in the SRE curriculum for parents of 8- to 10-year-olds, although reduced confidence for one mother. Conclusions: Familiarising parents with materials has the potential to enhance SRE, by improving coherence between educators' and parents' messages to children about sex and relationships, increased discussion of SRE topics in parent-child conversations and reduced parental anxiety about topics such as sexual orientation. Future challenges of involving fathers, scalability and sustainability highlight the dilemma of how best to enable parental choice or make equalities interventions.