Research on adolescent sexual and reproductive health (SRH) in sub-Saharan Africa is heavily focused on preventing unintended pregnancies and preventing HIV infection. However, very little of this work focuses on, and actively targets, boys and young men. Gender-transformative approaches, or approaches that seek to shift gender norms and power relations, have been hailed as one way to disrupt underlying factors that can lead to poor health outcomes and drive HIV infection and adolescent pregnancy. Applying a gender-transformative approach in South Africa and Lesotho, across two low-resource settings with very high rates of both HIV and adolescent pregnancy, our research aims to meet an urgent need for localised solutions and do so in an innovative and inclusive way. The aim of this study is to address the evidence gap by adapting the If I Were Jack programme for use in South Africa and Lesotho, under the name If I Were Thabo. The original programme, developed in the UK, is a group-based intervention delivered to adolescents in educational settings, which includes a culturally sensitive interactive film about an adolescent who discovers that his girlfriend is unexpectedly pregnant, and a guided discussion about how participants would feel and react in his position. The programme is accompanied by educational materials and sessions for adolescents' caregivers, and has been shown to be acceptable and cost-effective in its current form. We propose to adapt the programme in two LMICs, South Africa and Lesotho, in partnership with adolescents, parents, teachers, community members and local experts. We will target adolescents aged 13-14, an age range where there is still potential to prevent sexual risk-taking before the majority of adolescents are sexually active, and before the increase in pregnancy and STIs reported in later adolescence. To develop and test the intervention, the proposed study will involve two phases. First, we will work with adolescents, their parents and caregivers, teachers, health professionals and other key community members to adapt and optimise the programme materials from the UK for use in South Africa and Lesotho. This will involve co-producing locally relevant and appropriate intervention materials in each site. Adolescents will work with researchers and filmmakers to write, cast and develop new films in each site, and advise on the acceptability of text-based material, and their caregivers will be consulted on caregiver-targeted information. Teachers, community group facilitators and healthcare professionals will provide feedback on materials designed for programme facilitators. In addition, we will ask adolescents and their caregivers to give feedback on some of the research tools that will be used in the next phase. Next, we will run a pilot of the programme within a feasibility cluster randomised trial to assess if the intervention implementation and evaluation design is feasible in both countries. As a part of this phase we will survey adolescents in schools and community groups, half of whom will be randomly chosen to receive the intervention and the other half of whom will continue with 'normal practice'. We will assess whether the questionnaires capture the necessary information on SRH outcomes for this group, including intentions relating to adolescent pregnancy, and HIV and STI infection. We will also evaluate whether the processes needed to implement the programme work well. After programme completion, we will interview adolescents and other stakeholders about their opinions of the programme and whether it is feasible to deliver in schools and community groups, and what will hinder or help the implementation in the two settings. Based on these results, we will decide if it will be feasible to do a larger trial of the intervention in both sites to see if the programme is effective in improving SRH for adolescents in these countries.