What's that tell you?
Here's a better idea, put them on commission. Pay elementary school teachers a small base and large incentives for each student they pass on with elevated reading and math skills.
For middle school, add civics.
Delete all sex ed as being expensive and properly the province of parents.
For high school, compare the levels of each freshman in the core subjects and pay for each based on competency levels upon entering the next grade, so you pay on net improvement, giving remedial teachers the greatest opportunity for incentive money.
Delete tenure at all educational institutions, we are all temporary-get used to it.
If salesmen were compensated like teachers, we'd have the best certified, laziest profession around. The country would be in a perpetual state of economic depression.
This bonus plan caused the test scores of low income black students to increase by 17% in one year. So naturally, the teachers unions are against it.