Adaptive function is an essential dimension in the diagnosis of neurodevelopmental conditions in young children, assisting in determining the pattern of intellectual function and the amount and type of support required. Yet, little information is available on the accuracy of currently used adaptive function assessments for preschool children. This study compares the results of 2 commonly used assessments, the Adaptive Behavior Assessment System (ABAS-­II) and the Vineland Adaptive Behavior Scales, Second Edition (Vineland-­II), on a group of 52 preschoolers referred for investigation of delays in development. Standard scores on the Vineland­-II were significantly higher than those on the ABAS-­II, but both assessment scores could be used to identify patterns of adaptive functioning that would require support. The amount and type of support required could not be determined by standard scores on either assessment. Greater consistency between scales and grading the level of support required was achieved using age equivalent scores. Age equivalent scores on individual subscales showed motor and preacademic skills that were consistent with developmental level; performance on all other subscales was lower than developmental level. This study supports the use of standard scores to identify significant impairment in adaptive function and age equivalent quotient scores to describe the amount and area of support required.