This article reports the results of a design research experiment in professional development for teachers of middle school mathematics. The authors report on how they developed their programs to account for three underlying conceptual challenges to their efforts: (1) the institutional contexts that teachers worked in, (2) the ways in which the learning developed in and through the community of practice, and (3) the relationship between teachers' learning in the program and teachers' teaching in their classrooms. Especially because of the different institutional cultures found in ISE versus