Introduction: Colombia has one of the highest fertility rates among adolescents in Latin America, which reflects poor access to health services and a lack of knowledge about contraception. Some laws support comprehensive sex education as a learning process that families and schools should provide.Objective: to assess the frequency of adequate knowledge and attitudes of acceptance towards contraception in students, their associated factors, and experiences on sex education.Methodology: Mixed methods study consisting of an analytical cross-sectional study and a qualitative hermeneutic phenomenological study. The former included students who completed a questionnaire with sociodemographic variables and surveys on knowledge and attitudes toward contraception. Focus groups were used in the qualitative study to evaluate students' and parents' sex education experiences.Results: 827 students were surveyed, of whom 52.3% had adequate knowledge about contraceptives and 80.1% had attitudes of acceptance. Talking with parents about sex education, receiving sex education, and being in the eleventh grade increased the likelihood of having adequate knowledge. Each year of age, being male, being a victim of forced displacement, and studying in a public school were associated with lower possibilities of attitudes of acceptance. Using condoms, compared to other contraceptives, was associated with less adequate knowledge and attitudes of acceptance (p<0.05). Experiences with sex education, contraception, and sexual and reproductive rights were three emerging categories in the focus groups.Conclusions: Sex education received by students is limited due to multiple barriers, so the need for high-quality, comprehensive sex education is emphasized.Funding: This project was financed by internal fundin:g for researchof the Fundación Universitaria de Ciencias de la Salud - FUCS. Minute No. 06 – 2020.Declaration of Interest: None of the researchers declare any conflict of interest.Ethical Approval: International and local ethical considerations were considered, some participants were minors, and sensitive issues were addressed. The project and the results were presented to all school boards. This research project was submitted to and approved by a Human Research Ethics Committee (0348-2020, August 10, 2020).