Drawing on the recently opened archive of the Pennsylvania Training School for Feebleminded Children at Elwyn, this dissertation traces the varied ways that psycho-medical experts, educators, and families with kin deemed feebleminded understood feeblemindedness and the purpose of institutional care. From the 1880s through the 1920s, developments in medicine, education, and psychology turned educability and curability into moving targets, fueling debates about whether a feebleminded child could grow into an adult citizen. Rooted in Greater Philadelphia, this dissertation traces these debates and their implications in institutions for the feebleminded, psychological diagnostic clinics, and special classes in public schools. It combines intellectual and social history methods to demonstrate how mundane needs and desires of both experts and non-experts operated at times in tandem and at times in conflict with eugenic ideologies. Everyday people contested and contained expert power to coerce and, by invoking a state obligation to provide care, bent expert priorities toward their own.