Objectives: Although sex and relationship education (SRE) represents a key strand in policies to safeguard young people and improve their sexual health, it currently lacks statutory status, government guidance is outdated and a third of UK schools has poor-quality SRE. We aimed to investigate whether current provision meets young people's needs. Design: Synthesis of qualitative studies of young people's views of their school-based SRE. Setting: Eligible studies originated from the UK, Ireland, the USA, Australia, New Zealand, Canada, Japan, Iran, Brazil and Sweden. Participants: Studies of students aged 4–19 in full-time education, young adults ≤19 (not necessarily in full-time education) or adults ≤25 if recalling their experiences of school-based SRE. Results: 69 publications were identified, with 55 remaining after quality appraisal (representing 48 studies). The synthesis found that although sex is a potent and potentially embarrassing topic, schools appear reluctant to acknowledge this and attempt to teach SRE in the same way as other subjects. Young people report feeling vulnerable in SRE, with young men anxious to conceal sexual ignorance and young women risking sexual harassment if they participate. Schools appear to have difficulty accepting that some young people are sexually active, leading to SRE that is out of touch with many young people's lives. Young people report that SRE can be negative, gendered and heterosexist. They expressed dislike of their own teachers delivering SRE due to blurred boundaries, lack of anonymity, embarrassment and poor training. Conclusions: SRE should be ‘sex-positive’ and delivered by experts who maintain clear boundaries with students. Schools should acknowledge that sex is a special subject with unique challenges, as well as the fact and range of young people's sexual activity, otherwise young people will continue to disengage from SRE and opportunities for safeguarding and improving their sexual health will be reduced.