I, too, have heard that VCI correlates more with school success and high achievement than does PRI. My younger dd, who has twice been tested on the WISC-IV, had VCI scores at the 99th and 99.7th on the two testings but she, too, has ADD and anxiety and really isn't as high of a performer and her VCI scores would predict. Comprehension was also my dd's outlier of a lower score on the VCI index both times.
We've never medicated and we haven't retested since starting alternative treatments for ADD (and don't know if we ever will retest) so I can't speak to what the scores look like in a medicated child. I'm told that the wild fluctuations we've seen in our kiddo on achievement and ability tests are not uncommon in kids with ADD/ADHD, though.
Your ds' WIAT scores, save for the math problem solving, do look quite a bit lower than I'd expect given his IQ. In our state, the IQ scores would qualify for a GT id, but he'd need achievement scores in the 95th percentile (composite math, reading, or total) as well to get that id. Plus, in some of our districts the id alone doesn't qualify you for any services unless your school/group achievement tests are consistently in the 95th percentile or above.
