I've been instructing for a few years now. There is one piece of advice that I would give in this situation. Don't be afraid to take control of the plane to save it. A lot of time the student may complain that you took control, they think they could have saved it, but in most cases would not have been able to. So if you are in doubt release the switch and take control. When you first start you will be taking the plane constantly, but as the student progresses you will take it less and less. But as the student progresses make sure that you do let him learn to recover the plane himself, it's a valuable skill that needs to be learned.

Hope this helps

Ken