I think you are all coming at teaching unions from a different perspective than Abge. Abge, if I recall correctly, is in Massachusetts. Some of the biggest critics I see here are from the Midwest and Canada. Teachers unions in the Northeast are different than in most other states. In New York, they're either the single largest - or one of the largest - donators to political campaigns at the state level. At the local level? Forget it, nobody is going to run a platform that's against the teachers.
In my hometown in (rural) New York, teachers could easily make $100,000 a year before retiring, and then have health insurance plus 70% of their salary FOR LIFE after retirement. It is the single cushiest job out there. ~60 hour workweeks, holidays off, summer off, you get snow days and will anyone ever fire you? Nope, so long as you don't molest any children. My high school was taken over by the state due to poor performance (25% dropout rate, abyssmal test scores, etc). Was a single member of the faculty or staff fired? The principal got moved to middle school. That's it.
So maybe it's different in other parts of the country. I know one of my former teachers said teachers in NY start off making almost $20,000 a year more than teachers in NC, where he started (again, not New York City, but upstate NY). No one will touch the teachers unions at any political level and they get the tax raises that they want every damn year. So I, for one, am in agreement with abge, though for different reasons. Its not to say every union is bad, but just teachers unions in the northeast can go rot in hell.