In defense of teachers' unions

Slate has a great piece on former DC schools chancellor Michelle Rhee, whose anti-union teacher witch-hunt was one of the reasons that Andrew Fenty lost reelection as DC's mayor. I've always been deeply skeptical of the anti-teachers' union argument - it strikes me that urban public schools have been so badly underfunded for so long that it's impossible to assess whether teachers are bad or not based on student performance, and if you just fire teachers without addressing the funding issue, you're not going to make any progress. This evidence backs this up:

If the ability to fire bad teachers and pay great teachers more were the key missing ingredient in education reform, why haven't charter schools, 88% of which are nonunionized and have that flexibility, lit the education world on fire? Why did the nation's most comprehensive study of charter schools, conducted by Stanford University researchers and sponsored by pro-charter foundations, conclude that charters outperformed regular public schools only 17 percent of the time, and actually did significantly worse 37 percent of the time? Why don't Southern states, which have weak teachers' unions, or none at all, outperform other parts of the country?

The secret is that like every public spending issue in the United States, education funding is wrapped up in issues of race and segregation. So until someone can convince affluent whites to spend money on poor blacks, you're left fiddling around the edges of the problem. Which in my view is exactly what Michelle Rhee was doing - just in a particularly obnoxious way.