From the same Hoagie's Page:
Most tests have subtests, and each subtest has a ceiling, sometimes the same as the other subtests, sometimes different, and these contribute to lowering the overall score if a child is not evenly or "globally" gifted. For example, the Wechsler intelligence tests were not designed to differentiate scores above 130 (WISC-R and WISC-III) or 145 (WISC-IV):
...
Sattler and Dumont continue to say that the WISC-IV is not a good measure for children scoring outside of 3 deviations from the mean. An average subtest score of 14 or 15 is 2 standard deviations outside the mean, an average subtest score of 16 or 17 is 3 standard deviations outside the mean. Sattler and Dumont do not discuss the use of the WISC-IV
