This paper focusses on the teaching of non-linguistic subject matters in a second or third language through bilingual education. We investigate how this specific educational framework influences the development of linguistic competence as well as disciplinary knowledge. Based on a large-scale corpus of classroom interactions collected in bilingual education programmes in multilingual Switzerland and touching on various disciplines (biology, history, physics, maths), our contribution discusses how situated knowledge is acquired through L2 and L1 language processing, and how the conversational strategies used by teachers and learners focus on form and content through the interaction of the two languages of education. Whereas, code-switching--here specifically the use of the mainstream language (L1) in an L2 educational setting--is often regarded as a learner-oriented facilitating strategy, we argue that it enhances the learner's "metalinguistic ability". Thus, code-switching relies on the conversational routines of bi/multilingual communication settings. It also deals with the opacity of the subject matter by making the new concepts more familiar in L2, and more salient in L1. Bi/multilingual discourse is argued to function as an interface between linguistic and disciplinary knowledge in the process of introducing concepts and making them operational at different levels of complexity. Other basic cognitive strategies--such as sorting information, categorisation, argumentative organisation--also benefit from the multilingual construction of knowledge in various disciplines. (Contains 1 note.)