This paper reports research findings relating to a recent initiative to build capacity and support professional learning among educators to meet the needs of English language learners in Ontario schools. Drawing on data from case studies of educator teams in 16 school districts, the paper explores whether and how collaborative inquiry promoted effective professional learning and enhanced student learning. In particular, these findings suggest that engaging in collaborative inquiry shifted teacher attitudes, perspectives, and beliefs about language in education, deepened understanding of students' bilingual learning processes, and generated openness to the value of home languages and translanguaging for content curriculum learning. The findings are illustrated with examples from classroom practice, and implications for teacher professional learning are discussed.