Welcome, gmama!
Your son posts some very strong scores, certainly some that would be considered GT range. He also has quite striking diversity among his cognitive and academic clusters. I hope the evaluator gave you some clear interpretive narrative to chew on.
My thoughts:
cognition: Firstly, no, the WISC-V is not supposed to measure only a unitary construct (g). This is because the field is not in agreement that such a unitary construct exists, or can be definitively captured. The -V respects Dr. Wechsler's initial pragmatic intent, and many of his original tasks, but also bows to the body of evidence supporting the contemporary Cattell-Horn-Carroll model of intelligence, with many more subdomains, or aspects, of cognition. The five index scores are an attempt to assess some of the more highly-valued and easily measured of the theorized major domains. g is important, but a single g-score (the FSIQ), without any domains, would obscure the strengths and weaknesses a child like your son might display.
Clearly, language is his strength, in the Very Superior range. It's not as clear whether processing speed is as great of a weakness for him, or if the same temperament or style (anxiety, perfectionism, EF-shift) that caused him to bog down correcting math fluency items was at work in symbol search. The discrepancy between the two processing speed subtests is such that I'm surprised the neuropsych didn't give him the supplementary PS subtest (cancellation), too, to try to tease out the reasons for low performance on SS, and possibly give a more reliable PSI. If we postulate that coding is more representative of his PS than symbol search (and the achievement fluency measures other than math would appear to bear that out), then PS and FR are both relative weaknesses, but not as weak as the index score initially suggests. VS is probably slightly underestimated, as both subtests are timed (BD is also a fine motor task, so more likely to track the fine motor tasks of the PSI). Did the NP provide any information on his timed vs no-time-bonus performance on block design? (Or any other error analysis/clinical scores.) If there is a significant difference, that might tell us whether speed (or lack thereof) adversely affected his scaled score. WM is weaker than VC, but not to an extent unusual among children with a VCI in his range.
What does it mean that FR and PS are relative weaknesses, in the Average range? The relative weakness in FR suggests to me that he probably does better with tasks and learning that have meaning to him, such as those with connections to his real-life experience, or for which practical applications have been presented. Decontextualized abstractions generally aren't a strength. Factoid and rote memorization are probably not preferred methods. Sometimes children with this profile are experienced by teachers as disruptive, because they have difficulty maintaining engagement when meaning is not integrated into instruction, and they may talk a lot, often apparently at cross-purposes to the lesson plan, in an attempt to create this meaning and applicability for themselves. I will say his verbal list learning was better than I usually see for kids who need context. I'd be interested to know how he remembered them.
Processing speed weaknesses have many potential meanings, one of which is simply poor sustained attention, which would fit the ADD diagnosis. Alternatively, fine motor deficits (and you mention handwriting) can be a factor.
He did equally well (Average/High Average) on both auditory and visual working memory, which supports the idea of possible slight low estimate on VS.
achievement: I gather this was the new WJIV?
Reading and math (other than the aforementioned math fluency) track pretty well with his VCI and FRI, which are the two cognitive indices most likely to predict them, among those provided. The aspects of written language which are least likely to be vulnerable to mechanical issues approach his VCI, while those with the most vulnerability are more like his (presumed) PSI. It would be interesting to know how he would have performed on the Oral Language battery of the WJIV, to see how much of the written expression may have been pulled down by the complications of translating language onto paper, which involves not only fine motor skills, but automaticity (one of the possible elements affecting processing speed), and many executive functions (e.g., planning, organization, sustained attention); EF is a critical area in ADD/ADHD.
My apologies if this all just makes it more confusing...please ask for clarification!
