In this paper, we describe an experience within mathematics teacher preparation that engages preservice teachers (PSTs) in Making and design practices that we hypothesized would inform their conceptual and pedagogical thinking. With a focus on the design of new tools to support mathematics teaching and learning, this Learning by Design experience has PSTs exploring at the crossroads of content, pedagogy, and Making. We report our findings of the variety of forms of knowledge that PSTs brought to bear on their design work. As the engagement and advancement of these forms of knowledge is essential to effective mathematics teaching, these findings suggest the promise of a making-oriented experience within mathematics teacher preparation coursework. [For complete proceedings, see ED581294.]