{"p"=>"Adolescents are at increased risk of developing mental health disorders, making mental health literacy a key component of early prevention and recognition. Although school-based interventions are considered effective, they remain insufficiently implemented within the French education system. This study assessed the impact of a universal school-based mental health literacy intervention, IDEO (Inform, Destigmatize, Evaluate, and Orient), on adolescents’ knowledge of mental health and support services. A pre–post comparative study was conducted in all high schools of the Aube department (France) between January 2023 and December 2024. The IDEO intervention was delivered by mental health professionals and educators through two interactive sessions. Students aged 15–16 years completed self-administered digital questionnaires before and after the intervention, assessing mental health knowledge, misconceptions, and awareness of available support services. Knowledge acquisition was measured using a score based on the number of 18 possible correct answers. Multivariable and sensitivity analyses were performed to identify factors associated with knowledge improvement. Paired pre- and post-intervention data were available for 2,480 students. The mean (SD) knowledge score increased significantly from 5.8 (2.6) at baseline to 8.5 (3.6) post-intervention (p < 0.001). Improvements were observed across all knowledge domains, although awareness of support services remained comparatively low (mean score 1.8 ± 2.2; maximum 9). Greater knowledge gains were associated with female gender, higher baseline knowledge, and awareness of the positive impact of sleep on mental health (p < 0.05). Students enrolled in vocational education showed lower post-intervention knowledge scores (p < 0.001). Overall, 93.7% of participants reported being satisfied or very satisfied with the intervention. The IDEO program significantly improved mental health literacy among French high school students. These findings support the integration of universal, school-based mental health education into the French educational curriculum."}