In brief - if you are looking at FSIQ, the GAI may be more appropriate.
To calculate, find the addendum regarding the GAI from the publisher. This will tell you the amount of discrepancy req'd to make it a statistically appropriate option AND how to calculate AND other goodies. This includes charts showing the % of children with types of discrepancies and specific groups - from asperger's syndrome to dyslexia, etc. About 16 special categories to see the breakdown of scores and percentile ranks.
For example - my son has a 22 pt discrepancy:
FSIQ 114
GAI 136
He scored lower than his ability on block design the first time because he opted to disregard the instructions and build his own more complicated design, so he got the first, easiest question wrong.
He also has convergence insufficiency, saccadic tracking disorder, etc and "the visual spatial orientation difficulties" that underlie dyslexia but hey - can't diagnose it because he reads waaaay above grade level.
So, yes, sounds like 2E. High ability/intelligence can allow compensation or masking of LD. You are lucky - his memory is awesome. My son's is so glitchy. My son fluctuates between "brilliant" and "seriously not brilliant.". When you see things that don't fit - you'll know. My son could make the most astounding connections and abstract thinking yet couldn't remember how to spell his last name or being able to read "yellow" easier than "dog". Knowing fractions and using them before he could count to 20. Just very uneven and atypical development are often cues.
Look at the lists of G/T though - they'll help, too, Personally, I look for quick understanding of concepts, creativity, inventiveness, and insight. Often subjective but you can compare between G and not G or even 2E.
Sorry about length,
A
