Dr. Mason has held clinical and leadership positions in community-based service programs, hospitals, treatment clinics, special educational programs, and state institutions. Dr. Mason was previously appointed as a Professor of Pediatrics at Georgetown University, where he led initiatives to address health care inequities for people with disabilities. He has been a strong advocate of human rights for people with disabilities, including deinstitutionalization of care, creating community integration services, and pursing alternatives to incarceration. 

Dr. Mason currently is in private practice providing diagnostic and clinical services for people with neurodevelopmental disorder, and intellectual disabilities, and related mental health support needs (www.bestversiongroup.com). He has conducted more than a thousand psychological evaluations using person-centered approaches, and is exploring the use of AI-assisted evaluations.