My DYS DS7 just finished first. He is not grade skipped and only recently turned 7. First grade was painfully easy and he kept telling me all year that he was not learning anything. His achievement scores are extremely high.
My DYS DD10 turned 7 just before she started 2nd grade. She was not grade skipped and she is also an extremely high achiever.
FWIW, we are in a high performing school system. Red-shirting is not unusual, but it is not epidemic either.
In-class differentiation, in our experience, has almost never worked.
In most cases (depending on the kid), I would want my already 7-year-old in 2nd grade - not first. Based on the fact that he is also gifted, I would definitely push to have him in second.
I am worried your DS would be bored to tears in 1st. I don't even know that you have to "sell" this one as a skip - more of a "placing him with the more appropriate grade" based on his calendar age and abilities. If you need to use the Iowa Acceleration Scale (IAS), though, it would help you advocate based on his age-for-grade. Best of luck!
