This study compared performance on the Functional Independence Measure for Children (WeeFIM), the Battelle Developmental Inventory Screening Test (BDIST), and the Vineland Adaptive Behavior Scales (VABS) in children with developmental disabilities. The three instruments were administered to 205 children with identified disabilities. All 205 children were tested using the WeeFIM instrument. The BDIST was administered to 101 children and the VABS to the remaining 104 children. Administration was counterbalanced and randomized across all three instruments. A proportional sampling plan was used to select the 205 children, who ranged in age from 11 to 87 months. A variety of medical diagnoses and levels of severity of motor, cognitive, and communication impairments were systematically included in the sample. Correlations (r) among subscales for all three instruments ranged from 0.42 to 0.92. Correlations for total scores ranged from 0.72 to 0.94. Analyses of potential moderator variables found no significant relation between age and severity of disability (r=0.05) or between socioeconomic status (SES) and severity of disability (r=0.21). Correlations with age were strongest for those subscale scores involving gross and fine motor skills. Correlations with SES and subscale scores ranged from 0.03 to 0.18. The three instruments provide important information regarding childhood performance in motor, self-care, communicative, cognitive, and social skills. The WeeFIM instrument requires less administration time and provides information directly relevant to evaluating functional outcomes for children with disabilities and their families.