The purpose of this study was to develop the scoring system for the Seating and Mobility Script Concordance Test (SMSCT), obtain and appraise internal and external structure evidence, and assess the validity of the SMSCT. The SMSCT purpose is to provide a method for testing knowledge of seating and mobility prescription. A sample of 106 therapists and 15 spinal cord injury experts contributed to the development of the scoring system. Validity evidence was obtained using 15 seating and mobility experts, 10 orthopedic experts, and 66 therapists with varying levels of seating and mobility expertise. Proxy measures of clinical expertise were used for external validity evidence since no criterion measures exist. The SMSCT was found to differentiate between seating and mobility experts' and orthopedic experts' intervention subtest scores (p = 0.04). The proxy measure of clinical expertise, seating and mobility hours/week, was found to predict SMSCT intervention scores (p = 0.002). The internal structure of the SMSCT may include evidence of reduced item performance but satisfactory convergent and discriminate evidence by construct definition. Although the SMSCT may be a promising approach for measuring seating and mobility expertise, limitations exist in the corrected content. Future application of the SMSCT should only be used after further development of the tool occurs.