Performance on the Kaufman Brief Intelligence Test-2 by Children With Williams Syndrome.

Holley et al. (2016) gave the Kaufman Brief Intelligence Test-2 to kids with Williams syndrome. They wanted to see if the test could show the full range of ability in this group.

The team tested children aged four to seventeen. They watched for floor effects, a problem where the test is too hard and scores bunch at the bottom.

The KBIT-2 worked well for most kids aged five to seventeen. It gave a clear picture of their verbal and non-verbal skills.

For the lowest-scoring four-year-olds, many hit the bottom of the scale. The test could not tell how low their skills really were.

Reus et al. (2013) found the same issue. They used an easier Bayley version for toddlers with motor or vision problems and raised scores without hurting validity. Both papers say: when kids function far below the test’s start point, switch to a simpler tool.

Levin et al. (2014) saw the same floor effect in gross-motor testing. Totally blind children scored at the bottom of the TGMD-II, just as the lowest Williams kids did on the KBIT-2. Again, the most impaired group needs a different test, not a lower score on the same one.

Gómez-Pérez et al. (2020) looked at the WCST-LP in autism and showed the opposite worry: their measure stayed valid even for very low-IQ kids. This contrast highlights that floor risk is test-specific, not population-specific. KBIT-2 has a low ceiling for the lowest ages; WCST-LP does not.

If you test a child with Williams syndrome who is four and very low-functioning, pick the Bayley or another floor-free test instead of the KBIT-2. For kids five and up, the KBIT-2 is fine and saves time. Always check the lowest items first; if the child cannot pass any, stop and move to a younger-level tool.