As a fellow instructor, I can certainly sympathize with your frustration. Give yourself a rest and maybe you will come back to it with a fresh perspective. If not, keep an eye out for someone else to pick up where you left off.

A popular past-time for teachers to complain about their students, but I know I've had the exact same problem. It really doesn't seem like anyone has the time to tie flies any more, or at least that is my explanation.

Good luck.