My younger son's GAI, obtained when he was 7, was 153. The older one's GAI at age 7 was 106. The older one has dyslexia and I know it (along with some vision and auditory issure) depressed his scores that first time around. Five years later his GAI was 140. I firmly believe that he is at least as intelligent as his younger brother and the dyslexia is messing with the scores.
I take the within 10 points of each other thing to mean that if you're seeing a large difference in IQ (particularly a 2+ standard deviation difference) between siblings that isn't explained by some obvious reason, it might be a good idea to see if the one with the lower IQ has a learning disability and/or sensory processing problem that is interfering with things.
