we are in a public school district in IL ... not the most challenging but one of the better districts, definitely not the bottom ones. And the objective for end of Kindergarten is add and subtract within 5. So starting 1st grade with a review of adding to 5 sounds about on track ... PAINFULLY so. I have a mathy kid who doesn't realize he's one. He learned basic addition to 10 from Vtech video games by the time he was 3.5 ... right after that he went into subtraction and addition to 20. When I ask him straight, he says he doesn't know the answer ... but then I see him do it all the time correctly. He just doesn't KNOW he can do it! lol ... same with multiplication. I've seen him do it, he just doesn't realize it. At one point I was worried about learning disabilities because he couldn't COUNT TO 20 ... yet he could add and subtract within 20? But one day he just did it right and the next day he was counting to 100 ... go figure?
Anyway, seeing our friends' kids who are the same age (DS is 4.5), I'm realizing most of them don't know what 1+1 is and the difference between him and "them" is starting to be more noticeable ... someone asks him "how old are you?" ...and he answers with "half of 8"

... and they walk away with a deer in the headlight look on their face.
He's supposed to go to K in the fall and be probably the youngest kid in class but knowing him, he will be bored and very disruptive to the rest of the class, so most likely he'll stay home and homeschool K, maybe even 1st grade and since he knows pretty much all K curriculum (except writing skills ... poor fine motor skills) and big part of 1st grade curriculum, we'll concentrate more on the fun things he wants to do ... he wants to draw construction plans and things like that ... Geometry for Kindergartners I guess?