This study presents a computerized assessment approach for evaluating a subject's pointing and selecting proficiency using computer input tools, to aid access tool selection for users with severe disabilities. The CAT system consists of three subsystems. The CAT system not only provides clinicians with an objective means of evaluating clients' specific mouse operating difficulties, but also allows them to compare the performance improvement made by a client make during the device selection and training period. The client's performance in each assessment task is assessed on the basis of speed, accuracy and efficiency. Besides introducing the CAT system, this study also describes an example of adopting the CAT system to assist a client to select a suitable pointing device.