The expansion of the school choice movement and greater flexibility allowed by Every Student Succeeds Act (ESSA) means that education governance is emerging as an important issue for school effectiveness. This longitudinal case study sought to gain an understanding of the implementation of a new governance structure, Policy Governance, in a private, independent school with deeply entrenched culture and patterns of behavior. Findings suggest an immediate positive influence on leadership and culture in the district, including a "trickle down" effect on shared leadership. However, challenges to sustainability indicate that even strict adherence to the model, unanimous support among board members, and strong board and administrator leadership may not be enough to support sustainability.