In Challenging the One Best System, a team of leading education scholars offers a rich comparative analysis of the set of urban education governance reforms collectively known as the 'portfolio management model.' They investigate the degree to which this model-a system of schools operating under different types of governance and with different degrees of autonomy-challenges the standard structure of district governance famously characterized by David Tyack as 'the one best system.' The authors examine the design and enactment of the portfolio management model in three major cities: New Orleans, Los Angeles, and Denver. They identify the five interlocking mechanisms at the core of the model-planning and oversight, choice, autonomy, human capital, and school supports-and show how these are implemented differently in each city. Using rich qualitative data from extensive interviews, the authors trace the internal tensions and tradeoffs that characterize these systems and highlight the influence of historical and contextual factors as well. Most importantly, they question whether the portfolio management model represents a fundamental restructuring of education governance or more incremental change, and whether it points in the direction of meaningful improvement in school practices. Drawing on a rigorous, multimethod study, Challenging the One Best System represents a significant contribution to our understanding of system-level change in education.