Abstract: Objective: The aim of this study is to evaluate the effectiveness of an affective-sexual education programme among 14-15 year-old adolescents and its impact on their perception of their health. Design: This is a quantitative, descriptive and prospective quasi-experimental study, employing various cross-sections throughout the school year. It constitutes an educational promotion intervention where a health blog serves as a supplementary component to the "Health and School" programme. This phase is assessed using specific tools designed to evaluate scales. The study aims to assess the programme's effectiveness in the areas of knowledge and attitudes related to sexuality, sexually transmitted diseases, and affectivity. Additionally, it aims to evaluate the intervention's impact on 292 secondary school students, divided into a control group (N=144) and an intervention group (N=148). Both groups belong to the same population and have undergone affective-sexual education interventions focusing on gender and sexual diversity perspectives. The assessment considers perceptions and behaviours related to knowledge about HIV and other STDs/STIs, attitudes towards HIV, health anxiety, and AIDS phobia. Cross-sectional comparisons between the control and intervention groups are conducted at three points during the school year: longitudinal study, baseline, at month 4, and at month 9 post-intervention. Methods: Median and interquartile range, Wilcoxon test for numerical variables and Fisher's test for categorical variables were calculated according to intervention group. Results: 53% of the students reported a very good perception of health, compared to 45% with a good perception. Boys reported a good perception of health (85%) and had perceptions of their physical appearance and health (p=0.023) and (p<0.001) in the intervention group. Differences were found between perceptions of physical appearance in the control group, which was close to normal (p=0.429). In terms of level of knowledge about HIV and other STDs/STIs, the most significant difference was found in knowledge about HIV transmission, which varied between groups. Conclusions: Early affective-sex education sessions have an impact on health perception and behaviours related to knowledge about HIV and other STDs/STIs, leading to reduced anxiety in adolescents. School nurses should focus on health promotion, prevention of sex-related diseases, healthy attitudes from a gender perspective and integrated affective relationships in all their dimensions.