Background/Context: Montessori education has flourished as an alternative approach to schooling for a hundred years. In the century since the first Montessori school opened in the slums of Rome, the movement has undergone sustained growth while simultaneously enduring efforts to modify the method in order to reach a wider audience. Despite Montessori's endurance and reach, the movement remains largely unstudied by educational researchers. This article presents a historical treatment of the method and the movement by treating Montessori as a case study of enduring and ambitious educational reform. Purpose/Objective/Research Question/Focus of Study: This article is an examination of the American Montessori movement as it has evolved over the course of the past one hundred years. Situated within an international context, the study traces the development of the movement from its failed introduction to the United States in 1991, to its rebirth in the 1960s, to its current resurgence as a time-tested alternative to conventional public schooling. Key questions revolve around Montessori's ongoing status as an influential yet marginal force in American educational reform. Research Design: This is a historical case study drawn from archival data, interviews with Montessori leaders and practitioners, and secondary sources (biographies, memoirs) generated between 1906 and 2007.