In this post, EduShyster interviews Eunice Han, an economist who earned her Ph.D. at Harvard University and is now headed for the University of Utah.

Dr. Han studied the effects of unions on teacher quality and student achievement and concluded that unionization is good for teachers and students alike.

This goes against the common myth that unions are bad, bad, bad.

Han says that “highly unionized districts actually fire more bad teachers.”

And more: It’s pretty simple, really. By demanding higher salaries for teachers, unions give school districts a strong incentive to dismiss ineffective teachers before they get tenure. Highly unionized districts dismiss more bad teachers because it costs more to keep them.

Dr. Han found a natural experiment in the states that abolished collective bargaining.

Indiana, Idaho, Tennessee and Wisconsin all changed their laws in 2010-2011, dramatically restricting the collective bargaining power of public school teachers. After that, I was able to compare what happened in states where teachers’ bargaining rights were limited to states where there was no change. If you believe the argument that teachers unions protect bad teachers, we should have seen teacher quality rise in those states after the laws changed. Instead I found that the opposite happened. The new laws restricting bargaining rights in those four states reduced teacher salaries by about 9%. That’s a huge number. A 9% drop in teachers salaries is unheard of. Lower salaries mean that districts have less incentive to sort out better teachers, lowering the dismissal rate of underperforming teachers, which is what you saw happen in the those four states. Lower salaries also encouraged high-quality teachers to leave the teaching sector, which contributed to a decrease of teacher quality.

Send this link to Bill Gates, Mark Zuckerberg, Arne Duncan, Michelle Rhee, and any other reformers you can think of.