Our study focuses on the effective implementation of "constellations," an institutional scheme for the in-service training of primary school teachers of mathematics and French, established in France since 2020. Based on a bottom-up training model, this scheme aims to encourage reflexive analysis of practices among peers, based on professional needs. In this article, we adopt a comparative approach in didactics in the French tradition to studying the processes of co-development of the work object, entitled 'problematic', by trainer and teachers during training situations in two constellations in different disciplinary and geographical contexts. The methodology combines different levels of analysis in order to document the work of trainers in association with management by leaders, and to ascertain their practical epistemology.