The challenges of teaching elementary mathematics and science, particularly in urban settings, have been well documented. While evidence exists that sustained professional development in mathematics and science can promote inquiry-oriented instruction and bolster student achievement, little has been written about the particular challenges associated with offering differentiated professional development through school-university partnerships. This paper examines the impact on student achievement and teacher practice when university teacher educators launched a 3-year science and mathematics professional development initiative in grades 3-5 at one of the university's elementary partner school campuses. Our intention was to create a ''constructivist'' professional learning initiative where the facilitator-researchers were responsive to teachers' ongoing needs and daily teaching challenges. After sharing results, we identify factors that may affect the ultimate success or failure of such initiatives in order to better understand how highly contextualized and differentiated professional development can be structured and sustained.