B.B.
Hi!
I just wondered if your son's vision has been checked? Maybe he's having problems seeing what's on the page and that's why he might lose concentration?
It sounds like your son has lots of energy, so maybe he could do some very physical activities right before sitting down to read for a while.
Try positive rewards too. Maybe let him play with a favorite toy or play a game with him if he can get through so many pages of the book, or take turns reading the pages.
Best wishes!
B.