Someone's weight has nothing to do with their abilities in gym class. I was never overweight, or even "chunky", yet I barely got by in gym for one major reason - APATHY. I really don't care to run around a track 15 times, I have little interest in softball or football, and I couldn't care less about vollyeball.
Now, when they let us use the tennis courts, GTFO of my way or end up with a "NNEP" tattoo on your forehead.
My gym class just started tennis about a week ago, and it's a blast. I've never had much interest in the sport, but after playing it I regret that we have to move on to flag football, of all things.