Much has been written recently about the role of talk in content-area learning, including science learning. However, there is still much to be learned about how teachers begin to engage students in the kinds of peer-to-peer conversations that help them make sense of their investigations in science and that advance their conceptual understandings. This study was designed to follow teachers as they received professional development about involving students in sense-making science talk and then attempted to enact the lessons of the professional development in an urban middle school science classroom. We present an analysis of the challenges that surrounded two teachers' efforts to engage urban grade 6 and 7 students in sense-making talk around science concepts, as well as the conditions under which students began to engage in connected and evidence-rich talk.