Addressing complexity in health promotion evaluation: a mixed-methods assessment of comprehensive sexuality education implementation in Italy

Background Despite advancements in complex systems theory in public health, the adoption of evaluation practices for complex interventions like comprehensive sexuality education (CSE) remains limited. Frameworks such as the Medical Research Council (MRC) guidance and Ketting et al.’s model offer useful tools for assessing CSE’s implementation and impact. In Italy, CSE remains inconsistently delivered, without integration into the national school curriculum and minimal evaluation. This study presents a mixed-methods evaluation of the implementation and short-term knowledge outcomes of EduForIST, a CSE intervention co-developed and delivered by Civil Society Organizations (CSOs) in Italian schools. Methods Using a mixed-methods design grounded in the MRC and Ketting frameworks, the intervention was carried out in 13 schools across four Italian regions (Lazio, Lombardy, Apulia, Tuscany) from February to November 2023. Schools self-selected via a call for interest. Students (aged 15–16) completed a 12-item satisfaction questionnaire and a 15-item knowledge pre-post-test. Quantitative analysis included Chi-square and logistic regression. Qualitative feedback was collected through open-ended responses to “What remained in your mind and heart after EduForIST?”, analysed using Mortari’s Empirical Phenomenological Method. Results A total of 585 students participated. Students reported strong interest in topics related to sexually transmitted infections (STIs), Human Immunodeficiency Virus (HIV) prevention, and consent. Gender identity and stereotypes were less frequently rated as engaging, despite showing knowledge gains. Students valued the open, respectful environment and the involvement of CSO educators, which helped facilitate discussions on sensitive topics. Higher proportions of correct answers were observed after the intervention across most areas, particularly on STIs (+ 35.9%), HIV treatment (+ 38%), and common misconceptions (+ 24.5%). Qualitative data revealed that students perceived the intervention as supporting self-awareness, empowerment around consent, and reducing stigma about discussing sexuality, fostering a care-based approach. Some students called for more interactive methods and additional sessions to explore complex topics. Conclusion In this study, school-based CSE was associated with observed short-term knowledge gains, while students’ accounts suggested that the intervention provided a safe environment for dialogue on sexuality. The findings stress the value of CSO educators to complement school-based education, and student-centred approaches. While the results are promising, limitations include selection bias, no control group, and short-term focus. Future evaluations should use longitudinal designs to assess behavioural outcomes. Overall, the study supports the development and evaluation of CSE programmes tailored to adolescent needs.