Classrooms around the world are becoming more multilingual and teachers in all subject areas are faced with new challenges in enabling learners' academic language development without losing focus on content. These challenges require new ways of conceptualizing the relationship between language and content as well as new pedagogies that incorporate a dual focus on language and content in subject matter instruction. This article describes three professional development contexts in the U.S., where teachers have engaged in language analysis based on functional linguistics (for example, Halliday & Hasan, 1989; Christie, 1989) that has given them new insights into both content and learning processes. In these contexts, teachers in history classrooms with English Language Learners and teachers of languages other than English in classrooms with heritage speakers needed support to develop students' academic language development in a second language. The functional linguistics metalanguage and analysis skills they developed gave them new ways of approaching the texts read and written in their classrooms and enabled them to recognize how language constructs the content they are teaching, to critically assess how the content is presented in their teaching materials, and to engage students in richer conversation about content.