WISC-IV and low IQ: review and comparison with the WAIS-III

The WISC-IV is likely to be in common use for the assessment of children with low
intellectual ability for the next 10–12 years. There are several concerns about its uses with
these children. Some children may not understand the instructions on some subtests, notably
for letter-number sequencing. There may be an unacknowledged floor effect that will result
in an overestimate of intellectual ability. The percentile ratings given in the manual are
inaccurate for percentiles below 1%. Evidence is presented that the WISC-IV may
systematically give lower IQ scores than the WAIS-III when assessing low IQ.