Abstract Building on and extending the frameworks of Teacher Language Awareness (TLA) in second/foreign language education and content-based/CLIL education (Andrews, 2007; Lindahl & Watkins, 2015; Andrews & Lin, 2017), this paper argues that effective teaching of academic content in an L2 requires a special kind of teacher knowledge that goes beyond simple addition of content knowledge and Knowledge About Language (KAL). Through an ethnographic case study, the researchers investigated the development of a science teacher’s TLA and teacher identity through her participation in a school-university collaborative project. Based on analysis of data from classroom observations, interviews, and lesson video stimulated commentaries, the researchers have developed a model focusing on CLIL teacher professional development as a collaborative, dynamic and dialogic process, where both teachers and teacher educators (TEs) are co-developing their knowledge and expertise in CLIL.