Devoted to public secondary education, this article, on the basis of ethnographic observations and interviews, analyzes how the transformations of the job and French educational policy redefine the political commitment and professional involvement of teachers. By the confrontation between professional socialization and social dispositions, it highlights three generations. More than an opposition between “old” and “young” teachers, this analysis shows that ways of involvement in the profession evolve during professional careers. In spite of a distancing from trade-unions, the teachers converge professional and political practices and so reproduce the potential for protest of secondary level teachers.