Everyone has hit on the key points already. Just to throw this in - a good instructor can't be afraid. When I first started flying, I flew with an instructor who would never let me fly the helicopter he was so afraid. He kept his hands so heavily on the controls I couldn't "feel" the helicopter. I don't mean for the first hour, but rather for three hours! How will your student ever learn how to fly? Needless to say I switched to a different instructor rather quickly, and he, on the other hand, would let my play around until I let things get out of wack before he would then correct the problem and explain what I was doing wrong. I learned rather quickly from him!