Teacher preparation programs will have a significant impact on the number of well-prepared physics teachers in classrooms around the country only if they are incorporated into departmental infrastructure, and do not simply depend on the volunteer effort of a small number of dedicated faculty members. Physics departments and university administrations must buy into the idea that they share some of the responsibility for addressing the nation's teacher shortage. Ultimately, sustainability depends on whether an institution is willing to devote substantial resources, in the form of faculty time, academic credit, and course reform support, to preparing the next generation of physics teachers.