Here are his subtests on WJ-III.
Reading fluency 128
Math fluency 112
Writing fluency 128
But he got a 162(!) in calculation...I've seen him write out all the multiplication tables quickly - he draws fast and his handwriting is great (they teach cursive in Montessori beginning in K)
Knowing what the WJ tests are testing might give a little more insight. There should be more of them than what you've got here, but based on these four:
Reading fluency isn't one I'm familiar with. Math fluency is a timed test of solving math facts. Writing fluency looks at essentially how well a child follows written conventions (punctuation, spelling, etc.) in writing short sentences. Calculation tests basic mathematical computation skills and is not timed as far as I know.
With some help from someone with more knowledge than I have on calculating WISC #s, FWIW, the scores you have on your first post of this thread would give him a VCI of 121, a PRI of 129, a WMI of 123, a PSI of 91, and a FSIQ of 123.
