The paper is situated within the theoretical and methodological framework of the the Joint Action Theory of Didactics (Sensevy, Le Sens du Savoir. Eléments pour une Théorie de l’Action Conjointe en Didactique, De Boeck, 2011; Santini et al., Science & Education 27:921–961, 2018) and within the practice turn line of research on epistemic practices in science education. We investigate classroom practice seeking to achieve the concurrent learning of English as a foreign language together with disciplinary knowledge of physics as a practice. Classroom life is analyzed closely in order to identify traces of effective learning through epistemic practices (Santini et al., Science & Education 27:921–961, 2018; Kelly, Linder et al.Östman et al.Roberts et al.Wickman et al.Erikson et al.McKinnon (eds), Exploring the landscape of scientific literacy, Routledge, 2011) in both foreign language proficiency and discipline learning (Cunningham and Kelly, Science Education 101:486–505, 2017; Cunningham et al., Science Education 105:255–280, 2020). Founded on a Wittgensteinian concept of language, the notions of thought style and jargon are posited as useful notions to identify the epistemic value of classroom activity. This is in relation to the epistemic potential inherent in the situations presented in class, as well as the culturally constructed body of knowledge pertaining to the epistemic potential at stake. The modeling of classroom activity in this research rendered visible aspects of classroom practice which were essential to understanding the progression of knowledge objectives in situ, as well as the epistemic value of an actor’s move in relation to the epistemic potential of a given context. The study concludes by positing the notions as efficient tools for both the analysis and design of learning environments, in particular for environments where language can be seen to be organically linked to the practice in which it is embedded (Collins, Social Studies of Science 41:271–300, 2011; Sensevy, G. Gruson, B., & Le Hénaff, C. (2019). Sur la notion de jargon. Quelques réflexions sur le langage et les langues. In C. Chaplier & A.-M. O’Connel (Éd.), Épistémologie à usage didactique. Langue de spécialité. (p. 35–52). Paris: L’Harmattan.).