Students with disabilities, recognized under Public Law 94-142, who are enrolled in special education are required to have a psychological reevaluation within a three-year or less time period (USDHEW, 1977). Thus, students who have been diagnosed as having a Specific Learning Disability (SLD) or Mental Retardation (MR) will periodically undergo a psychological assessment that will include some form of intelligence test. In the initial evaluation, the intelligence test most likely to have been administered was the Wechsler Intelligence Scale for Children-Revised (WISC-R, Wechsler, 1974; Reschly & Wilson, 1990). Upon re-evaluation, however, readministration of the WISC-R may be unnecessary for two reasons. First, if test data subsequent to the initial evaluation are supportive of the original diagnosis, then administration of the same IQ test may be a less than wise use of limited school funds and professional and student time. Second, unless educational programming for a student is dependent on a new IQ score, administering the WISC-R would not assist school personnel in developing instructional strategies.
Even though readministration of the WISC-R might be unnecessary in a reevaluation, some form of assessment has been deemed essential (USDHEW, 1977). Because of limited resources and time demands, there is a need for assessing intelligence in a shorter time period than that permitted by the Wechsler scales. One such instrument is the Kaufman Brief Intelligence Test (K-BIT; Kaufman & Kaufman, 1990) which purports to assess intelligence. Comparable to the WISC-R, the K-BIT provides three scores: A Composite or IQ score; a Vocabulary subscale (similar to the WISC-R Verbal IQ); and a Matrices subscale (analogous to the WISC-R Performance IQ). The K-BIT and WISC-R scores have the same mean and standard deviation of 100 and 15, respectively.
Use of the K-BIT in special education assessment raises one crucial issue for students who were diagnosed with a disability and enrolled in special education with IQs obtained from use of the WISC-R. Because test scores differ between tests for several reasons (Bracken, 1988), including recency of test publication, using the K-BIT as the intellectual measure in the reevaluation has the potential to affect eligibility decisions. Thus, the extent to which K-BIT scores are comparable to scores on the WISC-R is important both for assessment specialists and for students with disabilities.
A CD-ROM search of Psychological Abstracts and ERIC revealed three studies in which differences in IQs between the WISC-R and the K-BIT were reported. The first study, reported in the K-BIT manual (Kaufman & Kaufman, 1990) on a sample of nondisabled elementary school students, revealed that the K-BIT and WISC-R were significantly related, r = + .80, although the K-BIT provided a Composite score that was approximately six points lower than the WISC-R Full Scale IQ. In the second study (Prewett, 1992a), a sample of 35 students referred because of academic difficulties yielded statistically significant correlations ranging from + .58 to + .92 between the three WISC-R IQs and their K-BIT counterparts. Corresponding to the study using nondisabled students who were not experiencing academic difficulties, the K-BIT Composite was approximately six points lower than the WISC-R Full Scale IQ. The third study (Prewett, 1992b), on a sample of 40 male incarcerated juvenile delinquents, also revealed significant correlations among the WISC-R and K-BIT scores. Unlike the previous two studies, however, the mean difference between the WISC-R Full Scale IQ and the K-BIT Composite score was only .45 points.
These three studies provide evidence that K-BIT scores are generally lower than their WISC-R counterparts. No study, however, examined differences in WISC-R and K-BIT scores for students already diagnosed with a disability. Moreover, none of the studies investigated the longitudinal relationship between these two measures for a clinical sample. …