There's no single individual credited with turning the Arapaho Indian boarding school (presumably referring to one of the several boarding schools that served Arapaho children, as there wasn't one single, universally known school by that name) into a "success." The very concept of "success" for these schools is highly contested. From the perspective of the U.S. government's assimilationist goals, some might point to superintendents or administrators who achieved high enrollment numbers or seemingly high graduation rates. However, these metrics ignore the devastating cultural and psychological harm inflicted upon the children.
The schools were designed to forcibly assimilate Indigenous children into white American culture, stripping them of their language, religion, and traditions. Any perceived "success" was measured against the flawed and harmful goal of erasing Indigenous identities. Therefore, no one can be rightfully credited with turning these schools into a success; their very existence was a failure from the perspective of the Indigenous children and communities they harmed.