Background: This paper challenges the dominant story of Protestant and Catholic conflict by illustrating the critical role that mission schools played in creating denominational consensus in the West. Focus: Protestant and Catholic missionaries cast aside their differences as they worked toward common goals to "civilize," Christianize, and "Americanize" natives on reservations like Rosebud. United as whites against indigenous "others," these predominantly female missionaries forged new, interdenominational conceptions of American identity through their work in western mission schools. Research Design: The article offers historical analysis and interpretation. Conclusions: Despite a long historiography emphasizing conflict between these groups, this study of a Protestant school and a Catholic school on Rosebud at the turn of the twentieth century provides new perspectives on the Americanization process at the center of schooling during this period. This examination of missionary education adds to our understanding of educative efforts among Native Americans in the late nineteenth and early twentieth centuries by illustrating how religion, and religious denominationalism, operated on the frontier. Against a long history of missionary work in the West and denominational conflict in the East, Protestants and Catholics alike affirmed their own "American" identity through their work on Rosebud.