BACKGROUND: School-based sexual and reproductive health programmes are widely accepted as an approach to reducing high-risk sexual behaviour among adolescents. Many studies and systematic reviews have concentrated on measuring effects on knowledge or self-reported behaviour rather than biological outcomes, such as pregnancy or prevalence of sexually transmitted infections (STIs). OBJECTIVES: To evaluate the effects of school-based sexual and reproductive health programmes on sexually transmitted infections (such as HIV, herpes simplex virus, and syphilis), and pregnancy among adolescents. SEARCH METHODS: We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL) for published peer-reviewed journal articles; and ClinicalTrials.gov and the World Health Organization's (WHO) International Clinical Trials Registry Platform for prospective trials; AIDS Educaton and Global Information System (AEGIS) and National Library of Medicine (NLM) gateway for conference presentations; and the Centers for Disease Control and Prevention (CDC), UNAIDS, the WHO and the National Health Service (NHS) centre for Reviews and Dissemination (CRD) websites from 1990 to 7 April 2016. We handsearched the reference lists of all relevant papers. SELECTION CRITERIA: We included randomized controlled trials (RCTs), both individually randomized and cluster-randomized, that evaluated school-based programmes aimed at improving the sexual and reproductive health of adolescents. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trials for inclusion, evaluated risk of bias, and extracted data. When appropriate, we obtained summary measures of treatment effect through a random-effects meta-analysis and we reported them using risk ratios (RR) with 95% confidence intervals (CIs). We assessed the certainty of the evidence using the GRADE approach. MAIN RESULTS: We included eight cluster-RCTs that enrolled 55,157 participants. Five trials were conducted in sub-Saharan Africa (Malawi, South Africa, Tanzania, Zimbabwe, and Kenya), one in Latin America (Chile), and two in Europe (England and Scotland). Sexual and reproductive health educational programmesSix trials evaluated school-based educational interventions.In these trials, the educational programmes evaluated had no demonstrable effect on the prevalence of HIV (RR 1.03, 95% CI 0.80 to 1.32, three trials; 14,163 participants; low certainty evidence), or other STIs (herpes simplex virus prevalence: RR 1.04, 95% CI 0.94 to 1.15; three trials, 17,445 participants; moderate certainty evidence; syphilis prevalence: RR 0.81, 95% CI 0.47 to 1.39; one trial, 6977 participants; low certainty evidence). There was also no apparent effect on the number of young women who were pregnant at the end of the trial (RR 0.99, 95% CI 0.84 to 1.16; three trials, 8280 participants; moderate certainty evidence). Material or monetary incentive-based programmes to promote school attendanceTwo trials evaluated incentive-based programmes to promote school attendance.In these two trials, the incentives used had no demonstrable effect on HIV prevalence (RR 1.23, 95% CI 0.51 to 2.96; two trials, 3805 participants; low certainty evidence). Compared to controls, the prevalence of herpes simplex virus infection was lower in young women receiving a monthly cash incentive to stay in school (RR 0.30, 95% CI 0.11 to 0.85), but not in young people given free school uniforms (Data not pooled, two trials, 7229 participants; very low certainty evidence). One trial evaluated the effects on syphilis and the prevalence was too low to detect or exclude effects confidently (RR 0.41, 95% CI 0.05 to 3.27; one trial, 1291 participants; very low certainty evidence). However, the number of young women who were pregnant at the end of the trial was lower among those who received incentives (RR 0.76, 95% CI 0.58 to 0.99; two trials, 4200 participants; low certainty evidence). Combined educational and incentive-based programmesThe single trial that evaluated free school uniforms also included a trial arm in which participants received both uniforms and a programme of sexual and reproductive education. In this trial arm herpes simplex virus infection was reduced (RR 0.82, 95% CI 0.68 to 0.99; one trial, 5899 participants; low certainty evidence), predominantly in young women, but no effect was detected for HIV or pregnancy (low certainty evidence). AUTHORS' CONCLUSIONS: There is a continued need to provide health services to adolescents that include contraceptive choices and condoms and that involve them in the design of services. Schools may be a good place in which to provide these services. There is little evidence that educational curriculum-based programmes alone are effective in improving sexual and reproductive health outcomes for adolescents. Incentive-based interventions that focus on keeping young people in secondary school may reduce adolescent pregnancy but further trials are needed to confirm this.