I did a brief spiel on Cesar Chavez for Hispanic Heritage Month, and in it I emphasized the role of the National Farm Workers' Association. My seventh-grade class, which often calls out anything I say which even hints at political overtones, asked me many questions which made it clear they'd heard that unions were bad. My eighth graders just wanted to know what unions did for me.
As I answered their questions, I tried to make it clear to them that I was a biased source of information, that everything I was going to tell them was pro-union, and that therefore I couldn't be trusted to provide the whole story. (It's more important that they know valid information when they hear it than that they like teachers' unions.) But it made me think again about what unions are, what unions do, and why unions are generally unpopular in the US and generally getting less so.
And then I came across this excellent post by Audrey Watters, about why almost everything they say about teachers' unions is wrong, or at least skewed. I would only add the following things.
When teachers' unions oppose reform, it is not because we (the teachers, and the members of the unions) are opposed to improvements. We are, however, opposed to being taken advantage of. Part of what unions do is make sure that their members' working conditions improve over time, or at least not get worse.
And part of the argument that a certain flavor of education "reformer" makes is that teachers do not deliver value for money. The obvious solution to this is for teachers to increase their work load and complexity by an undetermined amount up to infinity without an increase in compensation in other areas. They call it--and this might be the worst part--accountability. (As this paragraph currently exists, it's awfully straw man. I'll find some examples--well, honestly, probably when I retire and write my book in the history of education at the turn of the century.) Unions (at their best) try to slow that process down somewhat, to force consideration of whether each change is going to actually improve the students' education experience, and whether it would place undue hardship on the teachers.
This is the take-away quote from this article: "If unions oppose merit pay, it isn’t because they want to just reward long-time teachers with higher pay, quality of instruction be-damned. It’s because what counts as “merit” in these proposals is not the same as being a good teacher."