Differentiating autism from other handicapping conditions, especially mental retardation, has been a constant problem for public schools. This study investigated the effectiveness of three instruments to discriminate autistic from trainable mentally retarded children. The Autism Screening Instrument for Educational Planning, the Childhood Autism Rating Scale, and the Diagnostic Checklist for Behavior Disturbed Children, Form E-2 were administered to 20 autistic and 20 TMR students. Discriminant analysis was used to determine the best linear combination of scores that would separate the two groups of children. All three instruments were found to separate the two samples of children. However, the CARS and the ASIEP provided for a greater separation of groups.

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A sample of 240 preschool children was used to assess the con struct validity of each of the McCarthy Scales of Children's Abilities (MSCA). Individual subtests were used in a stepwise regression analysis of MSCA scales. This analysis supported McCarthy's con struct of the General Cognitive Index (GCI) as well as the Verbal and Perceptual-Performance Scales. Construct of the Quantitative Scale was vague. For this sample, neither the Memory or Motor Scale construct was documented. This study indicated that clinical interpretation of the GCI may be warranted, but diagnostic use of the Memory or Motor Scales with preschool children should be avoided.

A correlational study of scores on the McCarthy Scales of Children's Abilities and the Wechsler Intelligence Scale for Children and the Stanford-Binet was conducted as an effort to demonstrate validity for the McCarthy scales. While the Binet IQ was related to the McCarthy Verbal score and General Cognitive Index, the WISC subtest scores and IQs were significantly related to McCarthy scale scores. The results indicated a lack of specificity among McCarthy scale index measures and an ambiguous definition of the General Cognitive Index.

A correlational study of the Detroit Tests of Learning Aptitude and the McCarthy Scales of Children's Abilities was conducted. In this sample of 111 children with a mean age of 5 yr. 8 mo., specific subtests or scales of each instrument were compared and analyzed. General ability or skill measures of both instruments represented the highest levels of correlation and shared, or common, variance. The only specific learning abilities assessed by both instruments and demonstrating common variance were determined in the motor and/or perceptual areas. Few relationships were determined for verbal or quantitative abilities as assessed by either instrument.