Despite the growing evidence on promising approaches to postsecondary instruction--and particularly on the benefits of student-centered, conceptually oriented instruction for underprepared students--there has been limited investment in supporting these approaches' widespread implementation. Most postsecondary instructors have limited training in pedagogy, and broad-access colleges have relatively few resources to invest in improving instruction and building high-quality curriculum. Moreover, the field has few documented models of scalable professional development that results in demonstrated improvements in teaching and student learning. To help address this gap in the literature, this paper describes the professional development model used in CUNY Start, a program developed at the City University of New York to support entering students identified as academically underprepared in literacy and mathematics. Using interview and survey data collected as part of a larger random assignment evaluation of CUNY Start, the paper explores how CUNY Start's multifaceted, coordinated system of professional development supports postsecondary instructors in enacting a student-centered, conceptually oriented instructional approach. CUNY Start's professional development model has several notable features: a staffing approach that values instructional expertise, an apprenticeship for new hires, coaching through classroom observations, and cross-college meetings. While this model is distinct from traditional approaches to professional development in higher education, elements of it can be applied in other higher education settings. The paper concludes by discussing how colleges and departments might structure professional development around a set of student learning goals, offer a system of ongoing supports, and create a staffing model that supports the development of instructional expertise. [The research reported here was supported by the Institute of Education Sciences, U.S. Department of Education, through Grant R305H140065 to MDRC.]