>You might be right about the hours the teachers work, but they're not doing it to avoid being fired. It is entirely self-imposed stress. Teachers have unions and tenure.

No, and no. Your perception of modern labor markets is dated and disconnected from reality. Schools are constantly facing budget cuts and a huge chunk of teachers aren't even full time (instead getting things like a 60% time position - less pay, no security, but enough hours that good luck working a second job). Those that get full time positions still face the elimination of their positions.