I've found that its important to have a goal for each training flight. At the beginning of training, its just executing level turns, both right and left at each end of the field. If the student strays to far from the path, I take the plane and get them back on track.

Once I'm convinced the student can safely keep the plane where they want it (on course and speed) we start working on approaches. If the student gets too far off the intended appoach path, I take.

Once we've learned approaches and can get lined up on the runway, we start working on landings. Again, when the student strays too far from the intended approach, I take it.

Now we get to the fun stuff. Once the student can safely land, they've got pretty good control skills, and we start working on recovery from stalls and spins. I do this before teaching them to take off. At this point, its usually pretty easy, and I'm not taking the plane back much at all.

Once they know how to recognize and prevent a stall, they're ready for take off, and this usually goes pretty easy at that point.

I generally tell the students that I'll take the plane when I get nervous. If I do take it, I explain exactly why, and give them a chance to understand what they should have been doing but weren't. I've never felt guilty about not letting a plane crash. When you get to the point that you're just standing there holding the trainer switch, its time to cut the cord.

Brad