Social validity is the extent to which procedures, goals, and outcomes are acceptable and important to end users and is not commonly addressed during assessment development. This article pilots a process of triangulating multiple methods to evaluate the social validity of a self-report assessment. These procedures were piloted using the Child Occupational Self-Assessment (COSA), a self-report of everyday activities for children with disabilities. This study collected COSA responses from 502 children with disabilities and conducted observations and interviews with 5 additional children with cerebral palsy. Data were aligned with social validity benchmark statements and integrated using data displays. Social validity was evaluated by examining congruencies and discrepancies in the results. Implications and the legitimacy of design decisions are discussed. (Contains 3 figures, 5 tables, and 3 notes.)