Teachers probably have more performance assessment than most other professions. They need to retain their registration which involves being of sound character and showing evidence of their teaching work being up to standard. A school can easily remove a teacher who is not good enough by not signing off on that part. Naturally that involves the school having evidence of assessment usually by department heads and the principle. Improvement plans laid out for those who need it etc. From what I have seen in recent years is some schools are reluctant to pull the trigger on the registration on poorly performing teachers as they know they will have a very hard time filling the position when they are already short staffed. It seems more and more time is spent on improvement plans and teachers getting conditional sign-off on registration.
If you want the best candidates to become teachers you need to make the profession attractive to the best candidates.