Scaling Up Instructional Activities: Lessons Learned from a Collaboration between a Mathematician and a Mathematics Education Researcher Joanna Bartlo, Sean Larsen, & Elise Lockwood Portland State University Mathematics curricula designed to focus on conceptual rather than procedural understanding often engage teachers in activities that are different from those they have previously experienced. This means that teachers often have a difficult time making sense of tasks from such a curriculum in the manner intended by the curriculum designer (Lloyd, 1999; Wagner et al., 2007). To that end, we report on a study in which we explored how a mathematician made sense of a research-based introductory abstract algebra curriculum while implementing it for the first time. A research mathematician, John, implemented an innovative research-based undergraduate introductory abstract algebra curriculum (Larsen, 2004). We met with John regularly for debriefing and planning sessions, collecting research data both from the classroom and our meetings. One of the most prominent themes that emerged was the complex role of mathematical content knowledge in the teaching of this type of curriculum. On the one hand, John’s extensive mathematical training was crucial to his making sense of curricular tasks and student thinking. On the other hand, however, we were able to identify a number of instances in which additional kinds of mathematical knowledge could have supported a more successful implementation of the curriculum. We argue that these kinds of knowledge are instances of what Ball, Lubienski, & Mewborn (2001) refer to as mathematical knowledge for teaching. Ball,