The purposes of this study were: (1) to compare the Pediatric Evaluation of Disability Inventory (PEDI) and the Mullen Scales of Early Learning (MSEL) as measures of change in children who have received Part C early intervention services; and (2) to compare the use and impact of environmental modifications on mobility, self-care, and social function in young children with and without gross motor delays. Thirty-four children who received early intervention services were stratified into 2 groups according to the severity of motor delay. The PEDI adn MSEL were administered 3 times; at an average age of 18, 31, and 53 months. Data were analyzed using a repeated-measures multi-variate analysis of variance. Effect size indices were compared within and between subjects on all scales. Between group comparisons were analyzed for the use of environmental modifications in PEDI activity areas and linear regression was used to determine if the use of environmental modifications was a significant predictor of function. The findings suggest that PEDI Functional Skills scaled scores are capable of measuring change in children with and without motor delays. The PEDI Functional Skill Social scale was found to be more sensitive to change than the MSEL Receptive and Expressive Language scales for children with motor delays. A higher proportion of children with motor delays used environmental modifications for eating, bed transfers and safety. A significant negative predictive relationship was found between the use of environmental modifications and PEDI scores. Using PEDI scaled scores may be an effective tool for measuring functional change at the group and individual level in children receiving Part C early intervention services. More research is needed to determine the impact of rehabilitative and child-based modifications on function in children receiving early intervention services.