The appropriateness of a consumer's seating and mobility system varies considerably depending on the competence, proficiency, and experience of the professionals assisting the user. At present, there is a scarcity of skilled and knowledgeable therapists to evaluate and recommend seating and mobility devices. There is also a lack of measurement tests available to evaluate the impact of educational experiences or clinical practice on the ability to make specialized clinical decisions about seating and mobility needs. The Seating and Mobility Script Concordance Test (SMSCT) is a new assessment tool, grounded in the hypothetico-deductive and schema theories of clinical reasoning. The test is designed to assess therapists by examining the organization of their knowledge, associations between items of their knowledge, and the adequacy of their clinical decisions as compared to expert consensus. This article describes the interview, test development, and content/item review processes used for the collection of content validity evidence. The iterative process employed and the appraisal of the content validity evidence that resulted in the final version of the SMSCT are presented. The SMSCT appears to be a promising assessment tool representing content within the domain of seating and mobility for individuals with spinal cord injuries. The process utilized to develop the SMSCT in spinal cord injury can be replicated for other diagnoses and domains.