BackgroundYoung people report higher levels of unsafe sex and have higher rates of sexually transmitted infections than any other age group. Schools are well placed to facilitate early intervention, but more effective approaches are required. Peer-led approaches can augment school-based education, but often fail to capitalise on mechanisms of social influence. The potential of using social media in sexual health has not been tested in school settings.ObjectivesFinalise the design of the Sexually Transmitted infections And Sexual Health (STASH) intervention; assess the recruitment and retention of peer supporters, and acceptability to participants and stakeholders; assess the fidelity and reach, in addition to the barriers to and facilitators of, implementation; refine programme theory; understand the potential of social media; determine design parameters for a future randomised controlled trial, including economic evaluation; and establish whether or not progression criteria were met.DesignThis was a feasibility study comprising intervention development and refinement of the STASH pilot and non-randomised feasibility trial in six schools. Control data were provided by students in the year above the intervention group.SettingSecondary schools in Scotland.ParticipantsStudents aged 14–16 years, teachers and intervention delivery partners.InterventionsThe STASH intervention was adapted from A Stop Smoking In Schools Trial (ASSIST) (an effective peer-led smoking intervention). Based on diffusion of innovation theory, the STASH study involves peer nomination to identify the most influential students, with the aim of recruiting and training 15% of the year group as peer supporters. The peer supporters deliver sexual health messages to friends in their year group via conversations and use of Facebook (www.facebook.com; Facebook, Inc., Menlo Park, CA, USA) to share varied content from a curated set of web-based resources. Peer supporters are given support themselves via follow-up sessions and via trainer membership of Facebook groups.Main outcome measuresThe primary outcome was whether or not progression criteria were met in relation to intervention acceptability and feasibility. The study also piloted indicative primary outcomes for a full-scale evaluation.Data sourcesPeer supporter questionnaire; observations of activities; interviews with trainers, teachers, peer supporters and students; monitoring log of peer supporter activities (including on Facebook and meeting attendance); questionnaire to control year group (baseline characteristics, social networks, mediators and sexual health outcomes); baseline and follow-up questionnaire (approximately 6 months later) for intervention year group.ResultsA total of 104 students were trained as peer supporters (just over half of those nominated for the role by their peers). Role retention was very high (97%). Of 611 students completing the follow-up questionnaire, 58% reported exposure to STASH study activities. Intervention acceptability was high among students and stakeholders. Activities were delivered with good fidelity. The peer supporters were active, representative of their year group and well connected within their social network. Carefully managed social media use by peer supporters augmented conversations. A primary outcome of ‘always safer sex’ was identified, measured as no sex or always condom use for vaginal or anal sex in the last 6 months. The intervention cost £42 per student. Six progression criteria were met. A seventh criterion (regarding uptake of role by peer supporters) was not.LimitationsSmall feasibility study that cannot comment on effectiveness.ConclusionsThe STASH intervention is feasible and acceptable within the context of Scottish secondary schools. The results support continuation to a full-scale evaluation.Future workSmall-scale improvements to the intervention, refinement to programme theory and funding sought for full-scale evaluation.Trial registrationCurrent Controlled Trials ISRCTN97369178.FundingThis project was funded by the National Institute for Health Research (NIHR) Public Health Research programme and will be published in full inPublic Health Research; Vol. 8, No. 15. See the NIHR Journals Library website for further project information.