The WISC is used not only as an intelligence test, but as a clinical tool. Many practitioners use it to diagnose attention-deficit hyperactivity disorder (ADHD) and learning disabilities, for example. This is usually done through a process called pattern analysis, in which the various subtests' scores are compared to one another (ipsative scoring) and clusters of unusually low scores in relation to the others are searched for. David Wechsler himself suggested this in 1958.
However, the research does not show this to be a very effective way to diagnosis ADHD or learning disabilities. The vast majority of ADHD children do not display certain subscores substantially below others, and many children who display such patterns do not have ADHD. Other patterns for children with learning disabilities show a similar lack of usefulness of the WISC as a diagnostic tool.
When diagnosing children, best practice suggests that a multi-test battery (i.e., multi-factored evaluation) should be used as learning problems, attention, and emotional difficulties can have similar symptoms, co-occur, or reciprocally influence each other. For example, children with learning difficulties can become emotionally distraught and thus have concentration difficulties, begin to exhibit behavior problems, or both. Children with ADD or ADHD may show learning difficulties because of their attentional problems or also have learning disorder or mental retardation (or have nothing else). In short, while diagnosis of any childhood or adult difficulty should never be made based on IQ alone (or interview, physician examination, parent report, other test etc. for that matter) the cognitive ability test can help rule out, in conjunction with other tests and sources of information, other explanations for problems, uncover co-morbid problems, and be a rich source of information when properly analyzed and care is taken to avoid relying simply on the single summary IQ score.
The empirical consensus is that the WISC is best used as a tool to evaluate intelligence and not to diagnose ADHD or learning disabled children. It can be used to show discrepancies between a child's intelligence and his/her performance at school (and it is this discrepancy that Educational Psychologists are looking for when using this test). In a clinical setting, learning disabilities are generally diagnosed through a comparison of intelligence scores and scores on an achievement test, such as the Woodcock Johnson III or Wechsler Individual Achievement Test II. If a child's achievement is below what would be expected given their level of intellectual functioning (as derived from an IQ test such as the WISC-IV), then a learning disability may be present.
The WISC-IV can also be used to assess a child's cognitive development, with respect to the child's chronological age. Using such comparisons with other sources of data, the WISC can contribute information concerning a child's developmental and psychological well-being. Very high or very low scores may suggest contributing factors for adjustment difficulties in social contexts that present problems in accepting such developmental diversity (or that cannot accommodate more than a certain level of high cognitive functioning.)