Teaching informatics with a socio-constructivist approach is the theme of the Professional Development (PD) proposal for teachers we present in this paper. This proposal is built upon the expertise we developed in the last few years by designing and delivering enrichment activities to school students, where constructivist strategies are used to let students discover informatics as a scientific discipline, and to promote computational thinking skills and problem solving competences. Starting from the analysis of teachers’ training needs, we structured the proposal into different units. We highlight their goals and contents, and illustrate some of the proposed activities. We held some training sessions to test our proposal; we report our findings and the feedback from the participants who amount to a total of ninety-five in-service and prospective teachers.