What are your son's reasons for not wanting to skip? I would recommend finding out what the reasons are, and then working on that. Is it friends? With our son, we promised to make play dates and sleepovers with his friends from the grade he was leaving, so he knew he wouldn't be losing those friends. Is he nervous about the challenges? You could get hold of some examples of what they'll be doing in the next grade to ease his fears.
Is sports an issue? With our son, he was not sporty in the least, and so that wasn't an issue (he said it wouldn't matter - he'd be staying at the bottom in sports, no change!) I'm not sure how to deal with the sports issue, but if it's a big deal I'd seriously consider that as a major factor when deciding about the skip.
