Student-reported quality and coverage of school-based relationships and sex education (RSE) vary, with gender/sexual-minority and disadvantaged students reporting poorer provision. Experience of RSE among younger adolescents is under-explored. We examined student-reported RSE coverage and priorities and how coverage, and sexual-health knowledge and awareness of services, varies between students and schools. The data came from a pre-intervention survey of students aged 12–13 years within a trial of an RSE intervention involving 50 English schools. There was most coverage of basic information, such as puberty and safeguarding. There was least coverage of topics more appropriate for older students, such as sexual relationships, and topics teachers might find difficult to broach, e.g. pornography and masturbation. Girls, gay/lesbian students, students of bisexual/other sexual orientation, minority-ethnic students and students reporting lower academic commitment reported lower coverage than others. Knowledge of RSE-related topics and sexual-health services was generally low. Boys, students of bisexual/other orientation and students with higher school commitment had higher knowledge. Students of bisexual/other orientation and students of lower commitment reported lower awareness of services. Coverage and knowledge did not vary with school-level attainment or local deprivation. Future forms of RSE provision should ensure content and teaching methods meet the needs of all students.