All professions involved in developmental disabilities have ethical standards that include a principle requiring that the individual professional provide competent treatment. In some cases, “competent” remains undefined (e.g., American Physical Therapy Association, 2000; Council for Exceptional Children, 1997). In other cases, competence is linked to scientific knowledge in the field. For example, the American Psychological Association’s Ethical Standards state, “Psychologists’ work is based upon established scientific and professional knowledge of the discipline” (American Psychological Association [APA], 2002). Physicians are expected to “continue to study, apply, and advance scientific knowledge” (American Medical Association, 2001). For various reasons, some of which we explore later, professional organizations typically avoid an explicit requirement that practitioners use only scientifically valid interventions. As a result, most of the professions involved in developmental disabilities tolerate clinicians who provide dubious therapies and managers who operate questionable residential, vocational, and community services.