Development of teachers' mathematical and didactic competencies by means of problem posing

International audienceThis paper presents a didactic experience with problem posing carried out with in-service secondary teachers. We propose a strategy specifically designed to modify a given problem and enrich its mathematical and didactic potential. The starting point is a teacher's class episode, which includes a previously designed problem as well as the reactions of the teacher's students when solving it. We ask the participating teachers to pose 'pre-problems' and 'post-problems', working individually at first and then in groups. The experience shows that problem posing contributes to the development of teachers' didactic and mathematical competencies