This paper focuses on a collaborative research project with a transformative aim in which the research team worked ‘with’ teachers, rather than ‘on’ them (Morrissette, Pagoni and Pépin, 2017). The research explores and investigates a bilingual French/English immersion programme at an elementary school in the East of France. This programme initiated in 2011 following the training of several teachers in the United States, in the context of the Jules Verne Program. The objectives of the research partnership were also to "open avenues" to new bi-plurilingual practices among the teaching staff within this immersion context. In order to reconcile the demands of the institution, the teaching staff and the researchers, a two-stage methodology was adopted. First a descriptive and comprehensive study of the particular situation of this school was carried out and then conducted empirical investigations were conducted, based on the most salient elements emerging from the initial work sessions with the teachers. The paper firstly presents the methodological protocol chosen for the research comprised of the following three alternating stages : co-location, cooperation and co-production (Bednarz, 2013). Secondly, the results of the analysis are discussed, in particular : 1) the teachers' willingness to act and to transform their practices and 2) the tension between confidence in their prior knowledge and experience, questioning of institutional injunctions and appropriation of scientific knowledge. The methodological protocole includes semi-structured interviews with the classroom teachers and institutional supervisors (Bailly, Choffat-Dürr, Lemoine-Bresson, Lerat and Mary, 2020), classroom observations, recorded collective self-confrontations and focus group interviews. They are based on topics that emerged during discussions with the researchers and work sessions dealing with selected theoretical contributions. After almost two years of collaborative field research, this paper intends to examine and evaluate the methodological choices implemented in this protocol. The results of the analysis show variability in the teachers’ capacity to implement activities which had been carried out in an American immersive context and their willingness to engage in new practices which conflicted with linguistic ideologies anchored in monolingualism inhibiting the development of plurilingual competencies and the valuing of home languages (Mary and Young, 2017).