Ray Fisman reports at Slate:
Firing bad teachers may seem like a rather obvious solution, but it requires some gumption to take on a teachers union. And cleaning house isn’t necessarily the only answer. There are three basic ways to improve a school’s faculty: take greater care in selecting good teachers upfront, throw out the bad ones who are already teaching, and provide training to make current teachers better. In theory, the first two should have more or less the same effect, and it might seem preferable to focus on never hiring unpromising instructors—once entrenched, it’s nearly impossible in most places to remove teachers from their union-protected jobs. But that’s assuming we’re good at predicting who will teach well in the first place.
It turns out we aren’t. For instance, in 1997, Los Angeles tripled its hiring of elementary-school teachers following a state-mandated reduction in class size. If L.A. schools had been doing a good job of picking the best teachers among their applicants, then the average quality of new recruits should have gone down when they expanded their ranks—they were hiring from the same pool of applicants, but accepting candidates who would have been rejected in prior years. But as researchers Thomas Kane and Douglas Staiger found, the crop of new teachers didn’t perform any worse than the teachers the school had hired in more selective years.
Some interesting comments on the Slate site too. Not everyone agrees that it is hard to fire teachers.