Yeah, I wouldn't worry too much about their level if their being skipped. I skipped second grade right into third with no prep whatsoever -- I *did* have to work a bit, which is why it was so great. It was the only time all through grade school when I had to apply myself for a few months.
If my ds6's school had granted him a grade skip (we tried hard and they just wouldn't), I wouldn't have done anything to prepare him. He'd have caught on pretty quickly -- and places where there were gaps that mattered (science, maybe) we'd have worked on at home if he wasn't able to cotton on at school.
