Don't sit
Or change where he is when he does certain things. There's no reason for him to sit at a desk if he's doing reading - maybe he's more comfortable laid out on the floor to do his math, and when you do read alouds for whatever subject you're working on, there's no reason why he can't have a little toy in his hand that he plays with quietly if it helps him concentrate a little more than just being fidgety. You can also break up your day a bit if it helps. Do a subject or two, then give him 20 min to go play and shake off the fidgets!