I have been spending time teaching my wife and kids how to hunt since they did not grow up hunting like I did. They all seem to enjoy it.
The problem comes in is that when aiming my kids and wife can't seem to close one eye to aim. Will shooting with a scope cure this problem. They have real trouble hitting well with open sites unless I hold one eye closed for them.
PROBLEM?? This is NOT a problem! It is better to keep both eyes OPEN, especially when using a scope. This permits the shooter to point the scope correctly at the target immediately, avoiding having to "search" around for it! Having trouble finding the target in the scope is a beginner's biggest problem! When the eye that is looking through the scope picks up the target, the magnification of the scope "automatically" makes that view the dominant one, then the shooter can either aim and shoot with both eyes open, or can close the other eye when starting the trigger squeeze.
I think you'd be wasting a lot of time & effort trying to "correct" a shooter by teaching him/her to close an eye!!
IF they are having trouble getting a good sight picture with iron sights, it is possible that the "off" eye is the master eye, in which case they may have to learn to shoot left-handed (or right handed, if they are left handed).