Just some thoughts from my recent experience with a similar situation- the huge gap between verbal and non-verbal may indicate a learning disability. I had a similar experience with my son taking the WISC and expected his verbal to be way lower than his non-verbal, but ended up like your son. My son too is a math guy. Looking over the subtests, the tester thought that my son has stealth dyslexia and we are in the process of getting auditory and vision exams to determine if he has auditory processing and vision processing problems which would be the reason for the dyslexia. Our tester said that block design was difficult for my son because he likely couldn't see or process things well enough to complete the tasks correctly.
We were completely blown away by this news and never ever would have said this about our son, btw. But now reading about stealth dyslexia, it totally fits.
