I agree with bh - If you can figure out why your DS is so against the skip, you can better prepare some arguments to convince him why it's a good idea, or you can find things to help make the downsides more palatable. Of course this is unknown territory for your DS, and he's going to be scared of some things. Talking it all out may help change his mind.
I still wonder why the IAS says all bets are off when the child is against the skip. I would give more value to this with an older child, but in early elementary, I would lean toward the parent and school staff knowing what's best.
I thought of another factor that helped convince our son that skipping wouldn't be so bad. He didn't want to lose his friends and doesn't like being in a situation with a bunch of strangers. As it turned out, our school had 10 classes of Kindergartners moving to 1st, so it was likely he'd be in a room full of strangers anyway. And we made lots of playdates with his friends (and still do).
