If you child is feeling antsy or has a case of the wriggles during practice, perhaps he just needs to MOVE while playing!
You could consider working in (legit) opportunities for him to shake out the ants in his pants using Tiny Decisions.
These could be coupled with music tasks like finding all the 'C's or other notes on the keyboard or strings. Or just plain chances to jump around or be a Dance Monkey!
The Tiny Decisions app is available for free from the Apple and Google Play stores.