This chapter explores two situated practices in an English-as-a-medium-of-instruction (EMI) university course in Catalonia. In a teacher-fronted format, the students are asked to publicly participate in the development of academic content, which gives rise to plurilingual practices. Using conversation analysis, this chapter examines how language alternations, as well as multimodal embodied resources (gesture, gaze, and blackboard sketches), favour student participation in knowledge-construction activities. Our analyses suggest that students mostly strive to comply with the EMI language policy yet draw from their plurilingual repertoires when focalisation in critical content so requires. Thus, language alternation and other multimodal resources promote student public participation and the interactive construction of knowledge based on two elements. First, the verification, through teacher questions and elicited responses from students, that the latter understand the contents. Second, the co-construction of knowledge based on student self-selections and their public contribution to the development of the activity. We conclude that plurilingual and multimodal resources favour student public participation and thus the co-construction of academic content in the teacher-fronted EMI classroom.