Re: a teaching mistake
Fantastic question, and one I think most of us who teach have encountered at least a few times.
The best way to handle it, or the way I would handle it?
I have done exactly as you have done.
Also, I have begun to explain WHAT the technique should be like as I am messing it up/unable to execute it before moving to another technique, and am quite clear that the technique does work, just that I am unable to, which I believe is an important difference.
As for switching ukes until finding one who can follow the technique, there is merit in that argument; clearly the teacher wants the students to see it fully executed, and that is worth pursuing....as long as it is not ego-based.