The 223 he’s been shooting has a classic 3-9 variable. It is a fast twist barrel, so maybe not a bad idea to just swap the scope and get him dialing.
IMO, that would be a great direction to go. However, it would help if you had one with a stock that fit him so he doesn't have to learn all over again as he gets older. A fast twist youth model or a collapsible stock AR would fit the bill. Don't discount the value of a good .22 in his size to teach the muscle memory you need and include the fun factor to keep him interested. A squirrel hunt or two might also be helpful to transfer the lessons to real world results...
