Although initially ideologically diverse, the charter school movement has become increasingly aligned with neoliberal ideology, which assumes that public services, including education, are improved through market forces, such as accountability, competition, efficiency, and managerialism. Yet little is known about how leaders of ideologically progressive charter schools sustain their founding pedagogical and political missions amid widespread market values. This qualitative case study of one progressive charter school in New York City investigates this phenomenon. Findings demonstrate that the school's enrollment, instructional, school governance, and community engagement practices moved toward market values as school leaders and board trustees prioritized attaining favorable test outcomes, garnering resources, and ensuring the renewal of the school's charter. Findings illustrate a neoliberal grammar of schooling, or powerful forces that led school leaders to move their practices toward market values, in turn constraining the realization of the school's founding progressive mission.