This PhD thesis examines issues related to the professional development of eight generalist pre-service teachers in the context of French-speaking Switzerland. The latter individuals were teaching beginners’ German to children in the 5^th and 6^th grades in the Swiss primary school system corresponding to the 3^rd and 4^th grades of primary school in some European countries and international contexts. It is hypothesized that the identity of these pre-service teachers evolves from that of everyday speakers to that of professional speakers when they teach German. Data from self-reported judgments of these teachers—analyzed through self-assessment questionnaires and explored further through semi-direct interviews—were triangulated with video recordings of lessons showing their effective teaching practices. The findings of this thesis highlight how these teachers’ perceptions of their fluency in German were linked to their status as professional speakers and to their complex relationship with the subject knowledge associated with this language and related teaching knowledge in a classroom setting. The main findings also show biographical variables of these eight pre-service teachers which influenced their fluency and competence in German in everyday situations as well as in their methods of teaching German at primary schools. These findings also outline a few prototypical teaching sequences carried out by these teachers which emerged from the detailed analysis of lesson plans and synopses or sequential and hierarchical summaries of lesson phases. Finally, the self-reported judgments of these pre-service teachers were interlinked with analyses of effective teaching practices which reveals the complex relationships to subject knowledge that these teachers have with the German language and related teaching knowledge expected in a scholastic context.