Considering the evolving and unpredictable job market, adaptability is an important skill for young adults. Such adaptability implies that schools need to teach key social competences, like communication, collaboration, or problem-solving. In this area, a gender gap has consistently been found, showing that boys display social competences less than girls. A large-scale nationwide multilab longitudinal experiment--the ProFAN project--was conducted in France among more than 10,000 vocational high-school students. Its primary goal was to develop and test an intervention promoting a range of psychological and psychosocial variables in vocational high schools, including social competences. This 2-year long, three-wave field experiment compared the effects of a cooperative learning method--the jigsaw classroom, that entails positive goal and resource interdependence--to two control conditions: one that involves cooperation with resource independence, and the other that remains business-as-usual. This article focuses on the differential development of perceived social competences of adolescent boys and girls over time, comparing the three pedagogical methods. Results of longitudinal multilevel modeling replicate the gender gap in perceived social competences and show that this gap widens with time. However, and most importantly, the analyses revealed that such widening of the gender gap was greater in the two control conditions than in the jigsaw condition, in which the evolution of boys' and girls' perceptions of social competences remained similar over time. Contributions to the understanding of the development and teaching of social competences in education settings are discussed.