I was speaking to a administrator at a gifted school recently and discussing my DS6s wisc profile in which there is also a big gap between PSI and other indexes. They remarked that most of their students have "average" PSI scores. That my DS with a PSI in the 90s was not going to be that different from many students. Still I would guess that most of their kids are "average" at 105 or 110 or something, not 80.
The symbol search subtest is reliant on scanning and quick response time. It is a timed test. There is not a big working memory component, no verbal influence. There is a hint of analysis in that you have to recognize and discriminate one symbol from another. There is minimal fine motor.
The coding on the other hand, while also timed, has a input from working memory. It is sort of like the symbol search plus remembering and juggling things in your mind. Also no real deep analysis or verbal thinking input. There is a larger fine motor component.
So it makes sense to me midwestmom that if your DS has sort of average fine motor skills, or average visual processing speed, or just average speed at copying type tasks (dictation of sentences for example) in general, that the symbol search subtest could be a 8. The 8 in itself is not terribly low.
Then if you add in the working memory being average he can't use that as a relative strength on the coding subtest. My DS had a 150 on working memory, and that was enough to push up his coding subtest to a 10 I think it was, can't recall exactly. (His symbol search was 8). What I'm saying is with the coding subtest there is no way for your particular DS to mentally compensate for the absolute fine motor/visual/etc.
Ideally the symbol search and coding really measure what they are intended to measure, how fast you can process and respond in a speed task. I'm assuming above that scores really reflect ability. But personality can influence it too, like with Cassmo451's DD. A child who stops to say anything at all to the tester during the 2 minutes can wreck their score. A child who says to themself that this isn't that fun, that it's boring compared to the fun quiz type questions will have a poor score. If you are a perfectionist and go slowly in order to make what you are copying look exactly like the key you will not do well. If you are anxious about whether or not you are remembering things properly in the coding, if you always keep checking back that will lower your score.
Both subtests I think probably favor "sloppy sprinters."
So that would be my first question, whether the scores really represent their processing speed. If they do well at things like quick spelling tests, mad math minute, video games with multiple buttons/keys to hit, etc then probably the scores are not a good estimate and instead reflect something else coming in.
Maybe there is a component of both things. Some test anxiety plus purely average fine motor type skills, for example. Testing with an OT might help tease out what component is fine motor. The OT we recently went to also looked at visual processing.
If the scores do truly show their ability in processing speed then like my DS there is probably a chronic feeling of frustration, a bottleneck getting their complex thoughts out, particularly on paper. A difficulty showing the full extent of how they think. At school with average working memory and low or low average processing speed they may not come across nearly as bright as they are internally.
With my DS6 who truly does have motor planning/fine motor issues, school tasks are a big issue. The other kids finish mostly faster and can get the rewards of that whether it's reading their own books they brought or some fun center activity. DS has to finish while watching other kids having fun. Homework takes him too long and we have had no choice but to accommodate for that, it's not fair to a 6 or 7 year old for them to spend their evening on homework. He's very much at risk of feeling like a failure in school and that's in a typical public school. In a gifted program I assume it would only be worse because they might assume a little greater ability to organize or work quickly.
