The logical answer to this question is ZERO. But in the world of negotiating contracts with teachers unions, you know the answer is never this easy.
Take, for instance, the case of Bay City, Michigan. As the elected officials of Bay City re-negotiate their contract with the Bay City Education Association (the local teachers union), they ought to use this opportunity to reconsider the school district's existing substance abuse provisions. As the Washington Examiner's Sean Higgins points out (via The Mackinac Center), the old contract allowed teachers to be caught drunk in class for up to five times before they can fired.
This might come as shocking news to some, but it's right there, plain as day on page 92 of the Bay City Education Association’s 2011-12 official contract. Here's a screengrab of the specific provision:
How about if a teacher is high on drugs while instructing students? Would you be surprised to know that this offense, too, warrants a second chance?
I wonder how many second chances a student would get if they showed up to school drunk or high... Oh, that's right. Zero.