No, I don't think you're being too pushy. It sounds like you have a good handle on the issues, and if this school won't work with you, I'd look at others.
We don't have your issue, my DS6 is in the middle of the year with his birthday, but my brother and SIL have this issue with their DS6. Their school convinced them to put him into 4yo K instead of real K last year for social reasons, because he has an August birthday, even though they knew he was advanced academically (no testing though). They're regretting it now that he's in real K this year. He's a behavior problem because he's bored, he's being labeled as immature although I think he's actually more mature than the other kids and is acting out, and the year has been a bad fit. My brother and SIL are upset with the school for recommending they hold him back, upset with themselves for listening to the school, and the year has not been a good one. As Kathie K said, you know what your son needs, so keep looking or pushing till you get it.
