The WISC results echo the concerns with the reasons for low processing speed scores that I mentioned above. He's had six measures that should reflect some aspect of processing speed: coding, symbol search, visual matching, reading fluency, math fluency, writing fluency. Performance has ranged from the border of Average and Below Average all the way up to Very Superior. That does not look like a true cognitive processing speed deficit to me. It looks more like there are other factors that interfere with consistent demonstration of his strong processing speed.
If we sort the tasks into fine-motor-heavy and fine-motor-light ones, we have, in the motor-heavy category: coding, math fluency, and writing fluency. Two of them were relatively low, in the lower half of the Average range, while writing fluency was High Average.
In the motor-light category: symbol search, visual matching, reading fluency. One was relatively low, in the bottom of the Average range, while the other two are stronger, in the High Average and Very Superior range.
Note that visual matching and symbol search are very similar tasks, involving visual scanning and discrimination. Strong performance on one, and weak performance on the other, suggests that the weaker subtest is not a complete representation of these skills. The primary differences between the two are that one uses symbols, while the other uses numbers, and that for SS, one knows what the search items are, whereas for VM, one must scan all of the items to find the matching pair.
Now let's organize these in another way. We can sort them into tasks with thinking, and those with little thinking. In the thinking category: reading fluency, writing fluency. A small amount of comprehension is required for the reading task. The writing task requires quickly formulating sentences using provided target words. His performance is quite strong when thinking is involved.
In the little thinking category: coding, symbol search, visual matching, math fluency (depending on one's grasp of mathematics; his very high reasoning scores and decent computation scores suggest that it is not the actual ability to do arithmetic that affects math fluency). The lowest scores are here, with the exception of symbol search. Coding and visual matching have in common the need for repeated re-scanning of the materials, with the potential for getting lost in the visual tracking. Symbol search has much more widely spaced lines, separated by visual frames, which makes it much easier to scan. Plus, there are specified target images, which reduces the number of scans one has to do. Coding and math fluency have in common the highest fine-motor demands. It would be good to check if his math fact automaticity is any faster when administered orally.
So my thought is, some of the areas that might benefit from further investigation may include fine-motor skills, visual tracking, and high stimulation needs (differential performance when cognitively engaged--has some relationship to ADHD and other executive functions). My suspicion is that more than one of these is involved. For example, let's say fine motor and cognitive challenge explain most of the differences. If his true cognitive processing speed is represented by reading fluency, it's in the Very Superior range. Add fine-motor constraints, and it drops 1.5 SD, to the High Average range (writing fluency). Take away the cognitive challenge, and it also drops 1.5 SD (symbol search). Do both, and it drops over 3 SD, to the downside of the Average range (coding, math fluency).
