No question VT first. My ds8 was born with visual deficits and SPD. He had vision therapy between 4-6 yrs old. We saw huge improvements and developments then. In Dec, I had him re-evaluated with another behavioral optometrist since we moved and ds is two yrs older but still has some residual visual deficits.
My ds8 is a very advanced reader too, but he, too, is disorganized, gets distracted, and wigges a lot if he's forced to sit and do 'schoolwork' for long stretches. I'm un/homeschooling him though so ds can take a lot of breaks or learn in much smaller chunks of time.
I definitely would do the VT first because I found that we're likely to get inconsistent scores again and not a true picture of his abilities until the visual/sensory issues are addressed. With ds, it's just a matter of time and maturity for him before things come together more. It could be a similar situation with your ds.
I really believe some kids just need more time for the senses to be fully integrated more. I've seen neurotypical developing kids taking longer too until things start to come together.
