Most pediatric orthopaedic interventions are intended to improve or preserve physical function, yet their outcomes have been assessed using primarily surrogate measures (e.g., radiographic indices) that may not accurately represent patients' function. Physical function may be more appropriately measured with activity-based scales, but these have been infrequently applied in surgical studies. The purpose of this study was to identify existing activity-based physical-function scales appropriate for pediatric orthopaedics, to present criteria useful for scale selection, and to discuss the special problems of measuring physical function in children. Twenty-one scales relevant to pediatric orthopaedics are described according to their target population, purpose, method of administration, content, and quality of standardization. These scales have been further classified according to a new taxonomy. The unique aspects of measuring physical function in children are discussed and include the effect of age and development, method of reporting, and question formats. Standardized measures of physical function based on physical-activity ability exist and should be used more frequently to assess pediatric orthopaedic interventions.