Ideally, I'd like him in 1st grade in the morning and K in the afternoon. He's easily able to fit in with older kids academically, has bonded with one of the 1st grade teachers who was a specialty camp teacher over the summer and could fit nicely into their curriculum. The 1st grade teachers are excellent at differentiation and I've observed them stretch as far as 3/4th grade math on an individual level.
Ok, in that case, save your money and to directly to the Principal, as Val suggested, in writing, and then suggest the solution verbally at the meeting that they set up after they check into your claims.
Your 1st/K solution seems very reasonable, for now, given that your son is still physically so young - why should he have to 'sit still' for a whole day this year?
If you want to look at it from a social point of view, he's best off moving to a full day of 1st, so he can have a 'home base' and be 'regular.' Most likely he will miss his K friends, but the sooner he has a chance to make friends in the 1st grade class, the longer he gets to enjoy them.
I'm glad to hear that your school is exception to the differentiation guideline, good for you! However, why not put him in 1st so he can do his 3rd grade Math with a few others who are also ready, compared to keeping him in K, and ensuring that he works alone?
I don't really follow the logic of thinking that your public school wanted to place him in 2nd for his test scores. Is the current 2nd grade class particularly weak? Usually the schools DON'T want to offer any acceleration so they can be assured of the high test score in K or 1st.
My hunch is that it's a lot for you to swallow that your dear 5 year old would make friends and be o.k. in a roomful of 8 year olds. And why not. You probably were a sane person some time long ago before becoming a parent. ((Humor alert))Who could imagine such a thing?
I can tell you that if being with 8 year olds is were he needs to be, better to start that sooner, rather than later.
Some parents are ok with the 5 amoung 8s, but blanch at the thought of 10 amoung 13s. Truth is that none of us has a crystal ball to see in the future if thier own actual 10 year old would be best off with 10s,11s, 12s, or 13s. The best indicator you have now is to try to set up a few playdates with bright 1st and 2nd grade boys and see if they hit it off.
DS12 was with kids last year that ranged from 6 months to 30 months older. ((One official gradeskip, Summer Birthday, and Redshirting)) Of course, he was the friendliest with the kid who was 30 months older. ((shrug)) Social stuff is really hard to predict...
Bottom Line: Since you are looking for a solution that involves two classrooms, it's time to bring in the Principal. Be sure to stress the emotional effect that 'K academics' is having on your child, so you don't look like a 'nutter.' If a phone call won't get you a meeting with the Principal within 2 days, send a written letter (not an email.)
Best wishes,
Grinity