My research takes place at the intersection of the various communities involved in mathematics education, including teachers, mathematicians and education researchers, and is concerned with ways in which these communities can learn from and with each other, through processes of boundary crossing. Currently, I am investigating this topic in the context of the RBMC project (Raising the Bar in Mathematics Classrooms). The project brings together researchers, teachers and teacher educators with the shared goal of promoting challenging problem-solving activity in middle-school mathematics classrooms.