The study reported in this paper examines the impact of the Ohio Statewide Systemic Initiative (SSI) on participating mathematics teachers. Quantitative data from 90 SSI-trained teachers and 400 teachers without training, along with qualitative data collected from seven SSI teachers who were visited in their classrooms are presented. Analysis of the quantitative data showed that SSI and Non-SSI teachers reported significantly different frequencies of reformed teaching practices and held significantly different views about the nature and pedagogy of mathematics. Qualitative data from the interviews highlighted that the SSI professional development experience, the ability to find creative ways to overcome lack of resources, and the teacher support networks formed as a result of their participation in the SSI were three major factors which enabled the SSI teachers to make significant changes to their teaching practices, and to sustain those changes.