It is interesting to note that some children with clearly incredible verbal comprehension (or other variable) skills, may test lower on those subtests of the WPPSI, than seem reflective of their abilities. In the case of partial WPPSI, such as ERB, the tester's session notes may carry weight and provide insight, in reading and interpreting results.
My child took the SB5 at 3.11yrs old and scored in the top of the 99%ile, the WPPSI one yr later, scoring in the same range there. It was interesting that the lowest scoring subtest was in verbal comprehension, while performance, non-verbal and others, were far above the registered scale. I didn't have an opportunity to discuss these tests/results with either tester, but found the session notes from the WPPSI tester to be clear and informative.
Here in ny, there may be a considerable additional fee to confer with SB tester, so there is little insight into the process, unless this is done.
The assessments made using these 2 tests seem to be applied in very different ways. I've also heard that the SB5 is more of a spatial assessment tool and truer IQ measure, while the WPPSI has been described as more of a readiness gauge or achievement test.
I've been skeptical about using results from such young children as a true measure of aptitude and potential abilities. That is the only reason I would have my child test again at a slightly advanced age. Otherwise, we've seen these tests and their results applied in some ways (for admissions, etc) that seem often inappropriate in such young persons.
....They should have worded the problem better. 
