School-based sex education is a promising medium for reaching many adolescents with fundamental health information and life skills that can prevent unintended pregnancies  and sexually transmitted infections (STIs) including HIV/AIDS [1–4]. A review of 83 sex and HIV education programs revealed that such programs can be effective in improving sexual behaviors among youth, both in developed and developing countries . These programs are effective in increasing knowledge, changing attitudes , delaying the first sexual experience [5, 7], reducing the frequency of sexual intercourse and the number of sexual partners [7–10], lowering pregnancy rates , and increasing condom or contraceptive use [1, 5, 7] among young people.
Adolescents’ premarital sexual activities are increasing in the countries around the world, many of which are risky, unplanned [11–13], and unprotected [11, 12, 14, 15]. Among Nepalese adolescents too, premarital sexual activities are on the rise [12, 16, 17]. Such activities make adolescents one of the most vulnerable groups for HIV infection throughout the world and Nepal is no exception [11, 18, 19]. Therefore, this group needs serious and timely attention and active intervention.
The government of Nepal has designed a school curriculum which provides basic education on adolescence, sexual and reproductive health for all students from grades six through ten . School-based sex education has the potential to improve adolescents’ sexual health knowledge , attitudes, and intentions in ways that can affect their sexual behaviors . Specifically, positive attitudes and intentions regarding sexual behaviors act as mediating or motivating factors contributing to positive sexual behaviors [5, 22]. Since school-based sex education can influence students’ knowledge, beliefs, and intentions regarding sexual health, it is important to fully explicate and address the social and cultural challenges of school-based sex education.
School-based sex education remains a challenge, particularly in developing countries like Nepal. It is severely constrained by social and cultural taboos on discussing sex, STIs, and HIV/AIDS at school [23, 24]. Most of the schools often entirely lack student-friendly and positive environment, and a formal guidance or counseling system for students to seek advice and support on sexual health issues [23–25]. Because the information students need and want to receive is often incomplete and insufficient, they are frequently dissatisfied with the quality of sex education provided in their schools [23, 24, 26].
Research demonstrates that teachers are often not properly trained and lack the necessary skills to teach sexual health topics [23, 25]. Students from India, Kenya, Nepal, and Korea alike felt that their teachers were unable to teach sexual health topics effectively, sometimes even simply being left idle during sexual health lessons [23, 24, 26]. From the teachers’ perspectives in Nepal, India, and Kenya, support was lacking from school principals, parents, and the community for educating students on sexual health issues [23, 24]. Overall, both teachers and students remarked on the lack of training, teaching aids, interactive teaching methods, and on the inadequate amount of time allocated for sex education [23, 24, 26].
Parents’ involvement and support can improve the effectiveness of health education programs , especially in schools that are providing sex education . Communication with parents and active parental participation in educating adolescents about sexual health issues can demonstrably influence adolescents’ attitudes and beliefs , and may also help to delay the onset of sexual relations  and promote safer sexual behaviors [29, 30]. However, many Nepalese parents have especially low levels of awareness on matters regarding their children’s education, and thus are often unaware of the conduct or content of sex education in the schools . They are also typically afraid that sex education may encourage their children to engage in sexual activity at an early age . Thus, it is difficult for parents and adolescents to discuss sexual health issues . Other common obstacles to effective school-based sex education are the poor quality of textbooks, the lack of teaching materials and resources, and insufficient time allocated for sexual health lessons [4, 17, 24, 32].
Despite substantial positive evidence on the effectiveness of school-based sex education, only a handful of studies are available on school-based sex education programs from South Asian countries. A few qualitative and review studies have explored the difficulties of providing school-based sex education in Nepal [23, 25, 31], but quantitative evaluation on school-based sex education is still lacking. Therefore, the association between school-based sex education and student attitudes and intentions regarding sexual behavior remains unknown. Our study thus aimed, first of all, to assess the students’ evaluation of school-based sex education. Along the same lines, the study’s second objective was to examine the associations between students’ evaluations of school-based sex education and students’ (a) attitudes toward abstinence and (b) intentions for safer sex. We hypothesized that those students who evaluated their school-based sex education experience as poor might have poorer attitudes toward abstinence and intentions for safer sex.