The current study was the first to analyze the effectiveness of Positive Attitude Secondary School (PASS) Social and Emotional Learning (SEL) program upon the self-perceptions (social, academic, and emotional self-concept and self-esteem) of secondary school students, with a nationwide sample. The study also compared how different levels of developers’ involvement (defined as “led“, “involved“or “independent“) in program implementation influenced its effectiveness. Nine-hundred-nighty-five participants (7th to 9th grade; Mage = 12.95, SD = 1.70) participated in this study, 789 students (37 classes) received the PASS SEL program and 206 (nine classes) took part in the control groups. The program was implemented by the programs’ developers in the programs’ original setting (Torres Vedras); by another team in another municipality (Cadaval), where the program has been implemented in the last two years (“involved“); and by new teams in six Gulbenkian Academies of Knowledge spread throughout Portugal (“independent“). Self-report questionnaires were administered before and after the intervention. The results from the repeated measures MANOVAs showed that students who participated in the PASS SEL program displayed statistically significant larger gains in social self-concept and self-esteem when compared with students from the control group. However, there were no statistically significant differences in program effectiveness between the different level of developers’ involvement in the implementation of the PASS SEL program. Altogether, the results support the effectiveness of the PASS SEL program in enhancing self-perceptions, even with different levels of developers’ involvement, which indicates the program is ready for further dissemination.