Catholic educational historians note that although preserving Catholic identity has been a constant in the mission of Catholic schools, their curriculum and instructional practices evolved in ways that were similar to public schools, thus enabling Catholic parents to select schools that were both faith based and modern. Since there is an absence of information about when and how this change in Catholic education began, this article documents its origin in the 1940s when Catholic educators joined a public school reform movement called "Life Adjustment Education." Once begun, there was no turning back, and Catholic educators participated in the major reforms of the next two decades, discipline-centered curriculum reform and humanistic education. Two case studies are presented to illustrate what reform-based Catholic schools were like in the 1970s, followed by a brief analysis of Catholic school participation in the contemporary common core state standards movement.