The resignation of Washington, D.C., Schools Chancellor Michelle Rhee concludes the latest chapter in the ongoing war between free-market education reformers and teachers’ unions. Many Rhee supporters blame union opposition for the electoral defeat of Rhee’s boss, Mayor Adrian Fenty, and see unions as the biggest problem in education. In the much-discussed documentary, Waiting for Superman , in which Rhee is painted as a heroine, Newsweek columnist Jonathan Alter declares, "It's very, very important to hold two contradictory ideas in your head at the same time. Teachers are great, a national treasure. Teachers' unions are, generally speaking, a menace and an impediment to reform." The dichotomy (teachers good, unions bad), which has been a staple of conservative rhetoric for years, has taken hold among the center-left as well. Like Alter, the director of Superman , Davis Guggenheim, is a self-described liberal who nevertheless paints unions as the central problem in urban education...