I wasn't looking at the KTEA scores when I was talking about the timed tests, just the WISC.

And he's probably so good at math because we have a very math-centric house. DH teaches college math full time, I teach college math part-time and the gifted math at their elementary school part-time, including his algebra 1 class this year. He has also always been extremely interested in math, from toddlerhood.