The aim of this article is to present a case study in the field of ESD for in-service teachers training conducted in a Swiss primary school. A Discursive Community of Interdisciplinary Practices (DCIP) has been created including researchers, teachers, and a pedagogical advisor in the context of ESD, focusing on the topic of chocolate. In this article, we discuss how the DCIP helped teachers to develop competencies in the field of ESD. Furthermore, we see how teacher training could lead to a transformation of teachers' practices, moving from a normative education to a more reflexive one. We present the collaborative research and its theoretical context. The analysis of focus group discussions evidenced an evolution of ESD teachers' points of view. The analysis of the teachers' comments highlights the potential of the methods implemented to help teachers to enter into the process of conceptualizing knowledge in terms of ESD.