Comparison of Ability-Achievement Discrepancies Among the Wechsler Individual Achievement Test, Woodcock-Johnson-Revised Tests of Achievement, and Wechsler Intelligence Scale for Children-Third Edition in a Sample of Students Referred for Evaluation of Learning Disabilities

Abstract

Under current IDEA definitions, a significant or severe discrepancy between intellectual ability and academic achievement is the primary criterion by which a student may be classified as having a specific learning disability. By recommendation of the Work Group on Measurement Issues in the Assessment of Learning Disabilities (1984), the most common method of determining such a discrepancy is to calculate the discrepancy between an individual's score on an individually administered intelligence test and his/her score on an individually administered achievement test using a regression-based formula to correct for the regression of IQ on achievement. Because two previous studies suggested that the Wechsler Individual Achievement Test (WIAT) produced lower scores in the areas of reading, mathematics, and writing than the Woodcock-Johnson-Revised Tests of Achievement (WJ-R ACH), the main focus of the current study was to determine whether the two achievement tests identify significant discrepancies consistently. Data was collected anonymously from the files of 79 students who had been administered the WIAT, WJ-R ACH, and Wechsler Intelligence Scale for Children-Third Edition (WISC-III) as part of routine initial and reevaluations. Correlations, differences in mean standard scores, and discrepancy agreement statistics were calculated. Correlations among WIAT and WJ-R ACH subtests and composites purporting to measure similar constructs yielded significant results. However, consistent with previous research, WIAT scores were significantly lower than WJ-R ACH scores in reading decoding, reading comprehension, reading composite, math reasoning, and written expression. The WJ-R ACH Dictation subtest produced significantly lower scores than the WIAT Spelling subtest. Furthermore, the WIAT produced significantly more discrepancies than the WJ-R ACH in the areas of Reading Comprehension, Written Expression, and Writing Composite. The clinical implications, limitations and future directions are discussed.

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