Matt Yglesias writes that although the teachers' unions may in some instances shift policies towards one's that give preference to teachers and not towards programs that benefit kids, on the whole teachers' unions are beneficial for schools. They bring in money for schools. He points to Southern states that have weak teachers' unions and have low public investment in schools.
Well, some yes and some no.
Strong teachers unions do not necessarily mean more public investment in schools. Urban areas in Northern states have strong teachers unions and weak public investment in their schools. Think of Philadelphia or Cleveland. Those schools are seriously underfunded. The teachers work in bad conditions for little pay. In addition, nearly every well-meaning reformer in those cities have had to deal with the teachers' unions putting up road blocks at every turn, when they want to bring in new teachers, fire the bad ones, or reorganize failing schools.
But if you take cities out of it and just look at states, I'm sure that there is a correlation between strong union states and high levels of public investment in education. Though I would really like to see that mapped out to be sure. But it's not clear that strong teachers' unions are responsible for a state's greater investment in education.
This would be a really interesting and very doable study. I wonder if someone has done it already.