The Activities Scale for Kids (ASK) is a self-report measure of childhood physical disability, that has excellent reliability (ICC = 0.97). The purpose of this study was to assess further the ASK's measurement properties. ASK questionnaires were completed by 200 children with musculoskeletal limitations (mean age, 10.1 years). Rasch analyses confirmed that all items measured the same construct and supported aggregation of a summary score. Validity of the ASK was demonstrated by a correlation of 0.81 (P