Human Immunodeficiency Virus (HIV) and Sexually Transmitted Infections (STIs) among youths represent an important public health challenge in developing countries. The incidence of HIV peaked in the 1990’s and saw a decline from 2005. What was done to prompt the decline? To answer this question selecting studies between 1990 and 2005 was appropriate to assess whether the drop in HIV incidence in developing countries was as a result of education interventions. School based interventions are widely used to change young people’s attitudes towards early sexual activity and to prevent the transmission of HIV/STIs, and have been implemented by countries across the world. Methods: Electronic databases were searched to identify studies in HIV/STI education interventions conducted in schools in developing countries published from 1990 to 2005. Studies from 1990 effectively gave a clearer explanation of whether education interventions contributed to the genesis of the decline. In addition to assessing HIV incidence, the reviewer also included studies performed on sexually transmitted infections (STIs) as knowledge on STI prevention could lead to preventing HIV transmission. Studies were eligible if they had an appropriate comparison group; published in English and full text retrieved. Twenty-eight full text articles were assessed for eligibility, 17 articles met the inclusion criteria and 11 articles were rejected due to, not addressing HIV or sex education programmes in schools or were abstracts only. The Cochrane Effective Practice and Organization of Care tool for randomized controlled trials (RCTs), non-randomized controlled trials (NRCTs) and controlled before and after (CBA) studies was used to critically appraise studies. Results: All 17 studies reviewed established positive effects on knowledge. Programmes have similar characteristics and were more effective if they were conducted by adults. Conclusions: The overall conclusion of evidence gathered was that curriculum based programmes on HIV and sex education could be effective in changing the behavior of young people in developing countries if conducted properly. They were also effective in increasing knowledge on problems associated with risky sexual activity among young people. Further research is needed to assess the long-term positive effects of such programmes in schools in developing countries.