I suspect this is an issue that will go away with stick time. How much time has the student actually spent in the air?

I like the idea of just getting them three or four mistakes high and telling them to go full on all the controls and see how easy it is to recover. It will take practice. The other technique to teach the student is to move the sticks slowly, but continue moving them until you get the desired response. You should be calling continuously out to the student at this stage to get them to move the sticks further. Get them to understand that when you say pull, it means pull more than you are. Same with right or left bank. Make this crystal clear on the ground before you take off.

Also, make sure they realize that you are there to prevent the plane from crashing. Let them get in to trouble intentionally and then recover the plane for them. Eventually they will learn to trust your abilities.

Brad