Aim  To investigate the relationships among the Gross Motor Function Classification System (GMFCS), Manual Ability Classification System (MACS), and Communication Function Classification System (CFCS) in children with cerebral palsy (CP).Method  Using questionnaires describing each scale, mothers reported GMFCS, MACS, and CFCS levels in 222 children with CP aged from 2 to17 years (94 females, 128 males; mean age 8y, SD 4). Children were referred from pediatric developmental/behavioral, physiatry, and child neurology clinics, in the USA, for a case–control study of the etiology of CP. Pairwise relationships among the three systems were assessed using Spearman’s correlation coefficients (r_s), stratifying by age and CP topographical classifications.Results  Correlations among the three functional assessments were strong or moderate. GMFCS levels were highly correlated with MACS levels (r_s=0.69) and somewhat less so with CFCS levels (r_s=0.47). MACS and CFCS were also moderately correlated (r_s=0.54). However, many combinations of functionality were found. Of the 125 possible combinations of the three five‐point systems, 62 were found in these data.Interpretation  Use of all three classification systems provides a more comprehensive picture of the child’s function in daily life than use of any one alone. This resulting functional profile can inform both clinical and research purposes.