Back Cover Blurb:

Boxing? Football? Track? Roly-poly Bertie determines to try them all, despite the snickers of Heeble High’s star athletes. “At least I’m in there trying.” says Bertie to himself.
Fumbling, stumbling, through one hilarious mishap after another, Bertie plods on . . . and comes through!

I read this as a kid, handed down from my mother. I got a real kick out of it.