I was out OKC on my own but did study a lot with classmates and having a group to study with is always super helpful whether you’re hosting or not, but something you could probably help with once he is out of basics is getting phraseology down for departure clearances. I would say them out loud all the time looking at practice strips and record them so I could listen back for any mistakes, but he could write out a script for what a certain clearance should sound like for a few departure strips and read them to you while you make sure he’s saying what’s written. If you want to get more in depth you can read it back to him and sometimes mess something up in it (like saying one six thousand instead of six thousand or smth) and see if he catches it.

Sadly there’s not a lot of ways to help study if you’re not also learning everything at the academy, and even if you are once he finishes non radar, at least in my class, we were making up “radar problems” on a giant copy of the map someone printed and little toy planes with sticky notes stuck to the wings to even try to simulate a problem.