The general expectation for many successful educational innovations is to "scale up" the project. Based on interviews with participating teachers, facilitators and administrators, this research shares findings from the "scaling up" stage of a federally funded mathematics project designed to help teachers reach a wide range of diverse learners. Drawing on a more nuanced conceptualization of scale, our findings suggest that scaling an intensive mathematics PD program is a complex enterprise that requires coordination among multiple stakeholders in a school system. In going to scale, researchers must unpack their assumptions about scale in order to inform their program design and their research methodology and fine-tune their support for essential stakeholders. [This paper was developed by The Center for Technology and School Change, Teachers College, Columbia University.]