STASH is a school-based peer education project that seeks to complement standard PSE provision in schools to prevent and reduce transmission of sexually transmitted infections (STIs) and improve the sexual health of secondary schools students age 14-16 in Scotland. The project will recruit peer-educators in six secondary schools, from among those voted as most influential by their peers. This has been tried, with success, in a school-based anti-smoking intervention (ASSIST), currently being rolled out across Scotland. Peer-educators (15-20% of each S4 year group) will participate in a 2-day training run by Fast Forward (Peer Education Specialists) and will receive follow-up support – via face-to-face meetings and social media – to deliver the project. Peer educators will use social media and face-to-face interaction to influence attitudes, knowledge and behaviour among their peers.