Mathematics teachers' identities profoundly influence how they interact with and position their students to learn mathematics. In this paper, we examine how a year-long teacher learning intervention supportive of student engagement in mathematics helped shift teachers' mathematics-related identities. We use an implied identity perspective as a theoretical lens to explore changes in what teachers perceive as legitimate ways of being as a result of their participation in the intervention. Data from pre- and post-intervention concept maps and focus groups with 15 grade 5-7 teachers of mathematics were integrated for this purpose. Teachers reported shifts in their identities, describing themselves as "facilitators," "learners" and "co-creators" of knowledge. We argue that such shifts in the mathematics-related identities of teachers can have practical consequences in terms of improving students' engagement, and in particular, their autonomy for learning mathematics.