The study investigated adaptive behavior, as measured by the Adaptive Behavior Inventory for Children (ABIC), in diagnosing mental retardation among elementary school age children who were referred for special education services. Specifically, the study attempted to determine whether or not those children diagnosed as not mentally retarded and denied special education services on the basis of the ABIC data were statistically different, on the variables of intellectual development, academic achievement, and classroom behavior, from those children who were diagnosed mentally retarded and accepted for special education services on the basis of the ABIC data. Further, the study investigated the relationship between adaptive behavior and the prediction of academic achievement in elementary school age children.