I've written about this before, but just for fun everyone should go to a local school board meeting and ask how many teachers got an "Unsatisfactory" performance rating the preceding year. The answer in every single case will be ZERO. What does that tell you? Professionals? Hardly.
You must be attending a helluva lot of school board meetings throughout the country to have made such a sweeping conclusion.
Having actually been employed as a teacher in the public school system, I can assure you that you are very much mistaken.
While I agree that it is very difficult to remove an "Unsatisfactory" teacher during the school year, it is very possible to not renew their employment contract for the next year.