Depending on how he is trying to mount the gun it could be a master eye issue. It is pretty easy to spot. Usually, the shooter will mount the gun and turn their head so that the outside eye is higher than the one behind the barrel. Sometimes it is different. So, go throught the master eye check. If he has an offside master eye, switch him over to the off shoulder now.
Second, I have taught some real bad shooters of shotguns to be very good shots. Many years ago, I learned primarily by chance, that the best way to go is by starting them with a .22 or pellet gun. And, let them shoot it ALOT. And, I mean ALOT. That will teach them to line up a gun and shoot it properly to hit a target. Make it fun. Shooting tin cans or plastic drink bottles with a .22 can be a hoot. They can start with a rest of some kind. Even sitting with some kind of bench rest to start. When that gets too easy then they will progress to standing. When they are making tin cans dance around at about 30-40 yards with a .22 the transition to a shotgun is easy.
And, yes I also agree with all the above about original shooting lessons. But, the right position and all will be MUCH easier shooting a simple little .22 than a shotgun. For a non-shooter, each shot with a shotgun is an event.
Regards, Jake
