A very large flying school at which I used to work, had two wheels up landing accidents in the space of three years (none before or after, so far at least). Both were during dual asymmetric circuit training, where instructors did not complete the landing checklist and ignored the gear warning from over-familiarity.
I wonder if anyone anywhere has suffered a wheels up incident simply as a result of negative training from fixed gear aircraft? I suspect not. If I'm correct, the "gear down" call in a fixed gear aircraft is statistically irrelevant. It just doesn't seem to be a common human factors error.
Much better IMO to teach students to set a standard power on base. If the attitude and power are correct but the aircraft is not descending as it should, it's a good clue that the gear and flap isn't where it normally is. This also focuses attention where it should be (power, speed and aim point) not on written checklists.