This study examined the construct validity of the Autism Classification System of Functioning: Social Communication (ACSF). Participants included 145 parents of children with autism (2–19 years). The degree of convergent and discriminant validity between parent reported ACSF and subscales from Social Responsiveness Scale 2nd edition and Behavior Assessment System for Children, 3rd Edition were examined against a priori hypotheses. We examined construct validity in the entire sample as well as in specific age cohorts. Our findings suggest that ACSF can provide a valid classification system of social communication ability in children with autism 2–19 years of age, and its two subscales may be used to examine different aspects of social communication ability.