Sorry if this is long, but my point is that I wouldn't count out abilities - sports, academics, arts, etc. - based on early performance.
My husband is a prime example of that. He was the smallest in his confirmation class and was not particularly coordinated. He was a September birthday and was pushed ahead.
As an adult he is taller than the average NBA player, with incredible hand-eye coordination, and a longstanding annoyance with his school system for pushing him ahead. He didn't have much of a chance to compete physically because, as he says, he was younger than a good chunk of the boys the grade
below him, and it took his body a long time to catch up. (He gained two more inches and 20 lbs the year after high school.) The higher curriculum wasn't a help either, because he was so bored and had such bad handwriting he simply refused to do any homework -- considering it beneath him to do mundane practice of things he already knew. He graduated with a nice C average from straight A's on tests and very little finished class or homework.
Of course, that's just anecdotal. I think, on the whole, it's better to support the academic needs than the physical needs when you can. I think it's really about whether the grade above will give enough of a curriculum boost to be worth the possible other issues, and whether they're mature enough to handle the transition (mine wasn't).
