Three persons with severe physical and cognitive impairments, residents of a facility for persons with mental retardation, learned to use switch-controlled assistive devices. Previous case reports have described the technology and techniques used to enable these women to explore their surroundings. Material was collected, organized, and analyzed in three sections: clients, powered devices, and treatment approaches. The purpose was to affirm tenets that often provide the basis for treatment when powered activities are used in occupational therapy with adults with severe impairments. Client enthusiasm, responsiveness, and stamina can be predictive of success in using technology. Powered devices can elicit a client’s drive for competence, aid therapists in assessing the cognitive level of adults with extreme physical disability, and allow persons with multiple impairments to interact with objects in their environment. When clients learn to use powered devices, success will be self-perpetuating. Persons with multiple impairments using powered devices are well served by conditional clinical reasoning.