Assistive technology (AT) devices enable people with disabilities to function in multiple contexts and activities. The usability of such devices is fundamentally indicative of the user’s level of participation in multiple roles and occupations. Seventy people who used power wheelchairs were interviewed using a novel tool, the Usability Scale for Assistive Technology (USAT). The USAT uses a human factors science framework to investigate the wheelchair user’s perceived independence in mobility-related activities within home, workplace, community, and outdoors in accordance with the characteristics of the wheelchair, environmental factors, and abilities and skills of the user to operate the wheelchair. Descriptive analysis of the data revealed usability issues with the use of power wheelchairs in all contexts. Users confronted far more significant issues within the community and outdoor environment compared with those at home and in the workplace. These issues have been elucidated and applied to an intervention framework with relevance to a multitude of AT stakeholders.