While teachers face new expectations for student learning and more equitable educational outcomes, instruction and assessment remain rooted in traditional approaches that are largely inequitable, culturally irrelevant, and intellectually disengaging, contributing to gaps in academic achievement across student groups (Darling-Hammond, 2010; King & Bouchard, 2011). The quality of teaching is the most important school related factor influencing student learning and more equitable outcomes (Elmore, 2004; Leithwood, Louis, Anderson, & Wahlstrom, 2004). Many current reform initiatives--high-stakes accountability, school closings and turnarounds, charter and voucher schools, teacher evaluations and pay based on student performance--do not engage directly with critical tasks of building capacity for improved teaching. This article describes an urban high school in the Midwest, where principal and teacher leadership promotes collaboration among staff resulting in teacher learning to strengthen the instructional core.