Using Chicago as a case study, this book provides a new historical analysis of Progressive-Era reforms to professionalize teaching and, to a lesser extent, the principalship. Drawing on a variety of sources and archive material from the 1890s to the 1930s, it juxtaposes institutional prescriptions, social images, and professionals' discourses and practices to stress teachers’ and principals’ various roles in and responses to professionalization, as well as the complexity of the professional models elaborated and put into practice during the Progressive Era. It contributes to recent research in history of education calling for a more nuanced and elaborate assessment of the reforms promoted and implemented at that period.