The objective of this study was to evaluate aspects of the validity and reliability of the Client-Clinician Assessment Protocol (C-CAP) Part I. C-CAP data for 103 people aging with disabilities in need of home modification services were analyzed using the Rasch rating scale model. The C-CAP Part I consists of a client self-report of ability in daily life tasks comprising three scales (independence, difficulty, and safety). The analysis demonstrated support for internal scale validity, person response validity, and person separation reliability of the C-CAP Part I, although the results differed among the three scales. The results of this study indicated that the C-CAP Part I has psychometric strengths and limitations. The instrument has the potential to be used in the home environment with people who are aging with disabilities. The C-CAP could complement already existing tools that are used to assess functioning in activities of daily living, especially regarding the focus on the clients' self-report of difficulty and safety in daily life at home and in the community.