Pré-publication, Document de travail: This paper shows that schools can foster the transmission of civic virtues by helping students to develop concrete, democratically chosen, collective projects. We draw on a RCT implemented in 200 middle schools in three countries. The program leads students to conduct citizenship projects in their communities under the supervision of teachers trained in the intervention. The intervention caused a decline in absenteeism and disciplinary sanctions at school, alongside improved academic achievement. It also led students to diversify their friendship network. The program has stronger effects when implemented by teachers who are initially more involved in the life of the school.