So much more than that even, so many are teachers must feel compelled to do what they must for the sake of their students. I know it's incidental, but the extra effort I see my own kids' teachers putting in without financial incentive is incredible. Education is a business where a lot of "employees" probably aren't doing the calculations around their pay-per-hour but rather are focused on the accomplishing the things necessary for their students success.
Maybe that's a long winded way of saying that I suspect a lot of teachers are bleeding hearts and do not closely manager their time or monetary budgets closely.