My son has never taken an individual IQ test but he did take CogAT in 2nd grade. IAS-3 treats the cogAT composite score as your IQ score(they suggest using the cogAT verbal score as your IQ score if composite is not available), even though the CogAT test provider emphasized that the cogAT composite is not your IQ score because of the low ceiling of 150. My son hit the ceiling of 150 on the composite as well as the verbal so I don't know if his actual IQ score might be higher.
Anyway short story long he skipped 2 grades and ended 8th grade with a 4.0 GPA. He also subject accelerated in math and science so is basically 4 years ahead in math and 3 years ahead in science compared to his age peers. Socially he adjusted quite well, made a few good friends in 8th grade even though he's physically smaller. Overall he's very happy with his grade skip and is looking forward to high school next year.
From my perspective though, I feel like I have lost 2 years with my son. Those 2 years just disappeared into thin air, I don't know where they went. So, if you are really close to your son, that's something to consider.
Also, I feel like he has lost his network of friends since Kindergarten. I know that he will build a new circle of friends when he starts high school but still, he used to be much more social. Also leadership became an issue as he's so much smaller physically compared to middle schoolers 2 years older, hopefully this will go away once he hits puberty in HS. He was a leader among his age peers in elementary. His birthday is in November so he was among the older kids in his grade level prior to the skip.
The most important thing to consider is how your son feels about it. My son really wanted to grade skip badly because he was tired of being bored in school all the time. Unless your son really, really wants it, don't do it, and even if he really really wants it, I wouldn't recommend more than 1 grade now. He can skip again later if needed. 6th grade (first year of middle school) is a good grade to skip as it usually doesn't teach much more than 5th.
