This prospective cross-sectional multicenter study assessed the relationships between Gross Motor Function Classification System (GMFCS) level and scores on outcome tools used in pediatric orthopedics. Five hundred and sixty-two participants with cerebral palsy (CP; 339 males, 223 females; age range 4-18y, mean age 11y 1mo [SD 3y 7mo]; 400 with diplegia, 162 with hemiplegia; GMFCS Levels I-III;) completed the study. The Functional Assessment Questionnaire (FAQ), Gross Motor Function Measure (GMFM) Dimensions D and E, Pediatric Quality of Life Inventory (PedsQL), the Pediatric Outcomes Data Collection Instrument (PODCI), Pediatric Functional Independence Measure (WeeFIM), temporal-spatial gait parameters, and O(2) cost were collected during one session. Descriptive characteristics are reported by GMFCS level clinicians can use for comparison with individual children. Tools with a direct relationship between outcome scores and GMFCS levels were the PODCI Parent and Child Global Function, Transfers & Basic Mobility, and Sports and Physical Function; PODCI Parent Upper Extremity Function; WeeFIM Self-care and Mobility; FAQ Question 1; GMFM Dimensions D and E; GMFM-66; O(2) cost; and temporal-spatial gait parameters. Child report scores differed significantly higher than Parent scores for six of eight PODCI subscales and three of four PedsQL dimensions. Children classified into different GMFCS levels function differently.