DS took the WPPSI when he was a young 5. The examiner did not do a good job of establishing trust, and DS was resistant from the very beginning. The scores were low, and they clearly do not correlate with DS's capabilities in the classroom (and elsewhere).

So I'm very skeptical of putting any stock in low scores. High scores probably are indicative of high native intelligence (as traditionally defined), unless the tests are gamed somehow, but low scores? I remain unconvinced they mean much.

Also, keep in mind the Flynn effect as a confounding factor for IQ testing across different tests:
http://en.wikipedia.org/wiki/Flynn_effect