Many want to pay teachers for performance, but what's performance? Do you measure performance as year-to-year progress in reading or as the instillation of a life-long love of reading? And not all teachers teach reading.
I don't remember much about my first music teacher in high school. I just have some vague visual memory of the classroom. I certainly don't think I was a better musician at the end of the semester than I was at the beginning.
However, I do remember him saying, "Anyone with intelligence can sing." Almost fifty years later I started voice lessons and have improved in fits and starts over a five-year period. If that high school music teacher is still alive, should the school district give him a bonus for performance now?