The study focused on the aptitude test performances of intellectually sub-normal subjects on the Nonreading Aptitude Test Battery (R-NATB) vs. the General Aptitude Test Battery (GATB). There were two research questions investigated: (1) Are there performance differences on the RNATB vs. GATB of borderline and/or mildly retarded individuals?, and (2) Is the Wide Range Achievement Test-Revised (WRAT-R) a better predictor than the Wide Range Scale (WRS) of R-NATB and/or GATB aptitude performances in borderline and/or mildly retarded individuals? Two groups were selected for the study - 80 borderline and 80 mildly retarded subjects, ages 15-25 years. Each group contained 40 subjects with high reading skills and 40 with low reading skills as determined by the WRS. The order of aptitude test administration was also controlled. The research data collection began in November 1984 and was completed in October 1987. The following were the major findings for borderline and mildly retarded subjects. ages 15-25: (1) individuals with higher reading skills performed significantly higher on the General Intelligence (G), Verbal (V), and Numerical (N) aptitudes on the GATB and R-NATB than those with lower reading skills; (2) generally, the GATB and R-NATB did not meet the established criteria for tests known to have acceptable levels of convergent and discriminant validity; (3) subjects performed higher on the General Intelligence (G), Verbal (V), and Numerical (N) aptitudes when taking the GATB in comparison to the R-NATB; (4) subjects performed higher on the Spatial (S), Form Perception (P), and Clerical Perception (Q) when taking the R-NATB in comparison to the GATB; and (5) neither the Wide Range Scale nor the Wide Range Achievement Test-Revised proved to be effective predictors of higher GATB vs. R-NATB aptitude performances in intellectually subnormal individuals. If the GATB or R-NATB must be taken, borderline and mildly retarded individuals would optimize their aptitude test performances if they would take the B-1001 form of the GATB so they could mark their answers in the test booklet instead of on an answer sheet. Furthermore, the WRS and WRAT-R are not adequate screeners for predicting optimal aptitude performances / Ed. D.