Dale,
I've instructed more students than I can even count and I have "passed the radio" on more than one occasion. I won't instruct that way any longer. Why? Because there are times when the student "thinks" they know more than the instructor and doesn't think they need any help, and won't hand the radio back. I've even had one student turn away from me when I tried to take the radio back. When the student thinks he knows more than the instructor then it's time for the instructor to walk away and let the student crash. One of the jobs of an instructor is to know when to take the plane back from the student, and when not to. Trust me here, I've seen plenty of times that the student thought they had it but if I hadn't taken the plane back they would have crashed. The bottom line here is the instructor needs to have the ability to take control of the plane WITHOUT the student being able to interfere.

Ken