Background: Young women, especially adolescents, often lack access to modern contraception. Reasons vary by geography and regional politics and culture. The projected 2015 birth rate in 'developing' regions was 56 per 1000 compared with 17 per 1000 for 'developed' regions.

Objectives: To identify school-based interventions that improved contraceptive use among adolescents

Search methods: Until 6 June 2016, we searched for eligible trials in PubMed, CENTRAL, ERIC, Web of Science, POPLINE, ClinicalTrials.gov and ICTRP.

Selection criteria: We considered randomized controlled trials (RCTs) that assigned individuals or clusters. The majority of participants must have been 19 years old or younger.The educational strategy must have occurred primarily in a middle school or high school. The intervention had to emphasize one or more effective methods of contraception. Our primary outcomes were pregnancy and contraceptive use.

Data collection and analysis: We assessed titles and abstracts identified during the searches. One author extracted and entered the data into RevMan; a second author verified accuracy. We examined studies for methodological quality.For unadjusted dichotomous outcomes, we calculated the Mantel-Haenszel odds ratio (OR) with 95% confidence interval (CI). For cluster randomized trials, we used adjusted measures, e.g. OR, risk ratio, or difference in proportions. For continuous outcomes, we used the adjusted mean difference (MD) or other measures from the models. We did not conduct meta-analysis due to varied interventions and outcome measures.

Main results: The 11 trials included 10 cluster RCTs and an individually randomized trial. The cluster RCTs had sample sizes from 816 to 10,954; the median number of clusters was 24. Most trials were conducted in the USA and UK; one was from Mexico and one from South Africa.We focus here on the trials with moderate quality evidence and an intervention effect. Three addressed preventing pregnancy and HIV/STI through interactive sessions. One trial provided a multifaceted two-year program. Immediately after year one and 12 months after year two, the intervention group was more likely than the standard-curriculum group to report using effective contraception during last sex (reported adjusted ORs 1.62 ± standard error (SE) 0.22) and 1.76 ± SE 0.29), condom use during last sex (reported adjusted ORs 1.91 ± SE 0.27 and 1.68 ± SE 0.25), and less frequent sex without a condom in the past three months (reported ratios of adjusted means 0.50 ± SE 0.31 and 0.63 ± SE 0.23). Another trial compared multifaceted two-year programs on sexual risk reduction and risk avoidance (abstinence-focused) versus usual health education. At 3 months, the risk reduction group was less likely than the usual-education group to report no condom use at last intercourse (reported adjusted OR 0.67, 95% CI 0.47 to 0.96) and sex without a condom in the last three months (reported adjusted OR 0.59, 95% CI 0.36 to 0.95). At 3 and after 15 months, the risk avoidance group was also less likely than the usual-education group to report no condom use at last intercourse (reported adjusted ORs 0.70, 95% CI 0.52 to 0.93; and 0.61, 95% CI 0.45 to 0.85). At the same time points, the risk reduction group had a higher score than the usual-education group for condom knowledge. The third trial provided a peer-led program with eight interactive sessions. At 17 months, the intervention group was less likely than the teacher-led group to report oral contraceptive use during last sex (OR 0.57, 95% CI 0.36 to 0.91). This difference may not have been significant if the investigators had adjusted for the clustering. At 5 and 17 months, the peer-led group had a greater mean increase in knowledge of HIV and pregnancy prevention compared with the control group. An additional trial showed an effect on knowledge only. The group with an emergency contraception (EC) session was more likely than the group without the EC unit to know the time limits for using hormonal EC (pill) and the non-hormonal IUD as EC.

Authors' conclusions: Since most trials addressed preventing STI/HIV and pregnancy, they emphasized condom use. However, several studies covered a range of contraceptive methods. The overall quality of evidence was low. Main reasons for downgrading the evidence were having limited information on intervention fidelity, analyzing a subsample rather than all those randomized, and having high losses.