This question originally appeared on Quora. 
By Matt Johnson, Teacher of Physics, Fighter of Fallacies
Okay, so here's the key thing for everyone to understand, in my humble opinion:
Not all states allow unions, and not all public schools in states with unions have unions. So the obvious thing to do if you want to see how big of an issue unions are in education is to look for evidence that places without unions are better off than those with unions.
You probably won't find any.
Above is an article talking about how bad the states without unions do in education (typically terrible).
So, stop right there, everybody, please:
This fixation on teacher unions is crazy, and it's really the classic case of a scapegoat. Whatever our issues with educating K-12 are, they most certainly aren't based on unions forcing us to have lower quality teachers.
In the grand scheme of things then, getting rid of tenure is not only not very important, but it's not even remotely clear that it's a good idea. I'm down to have that discussion about it being a good idea, but only if it's first relegated to the level of importance it deserves, which means we first need to talk about what the actual issues are.
And here's the stunning truth: The general public is now convinced that teacher unions are the primary reason why are schools are so bad, but they have no understanding at all of whether our schools are actually bad, nor do they seem to think that they need a shred of such knowledge before advocating a nation-wide revolution.
This, by the way, happened half a century ago too, when the USSR launched Sputnik. Mass American panic. Calls for overhauling the entire system - which was eventually done. It might have had good effects down the road, but the same educational system that was blamed for us "losing" on Sputnik produced the scientists and engineers who won the Moon Race. Obviously, the panic was not based on anything rational.
So what's the issue? Why do we think schools are so bad?
Is it the international assessments that rank us so poorly? Consider the USA vs your typical Asian country that does great on them:
1. The USA gets tons of immigrants who don't speak English. This is a huge challenge that homogenous countries don't have to deal with.
2. The USA forces everyone to go to high school, which means we're comparing our average student to other countries' best students.
3. In many cases at American grad schools, there are large swaths of foreign students who have quite a bit of trouble with anything outside of their area of expertise, and have trouble period wading through the process of innovative and creative work.
4. We now have an entire field of study on what makes students learn better in terms of pedagogical strategies, and US classrooms have these strategies implemented far more and far more successfully then a typical Asian country will. These other country's are oftentimes still using techniques akin to what you get in a college GE with several hundred students.
So even if we grant the foreign students are learning better, it's not because the teacher in front of them is a better teacher.
Of course that doesn't explain how we fell from scoring the best in the world to where we currently are, but ... we NEVER WERE the best in the world by these metrics.
Isn't it amazing, the arrogance of the American who simply assumes that if we aren't #1 at something, it's because something JUST happened that ruined everything?
Last, to respond to the insanely low rate of teachers getting fired and people admitting that in practice, principals are finding it too hard to fire bad teachers:
There's truth in that. I'm not against change here, but when people say "kill tenure," to me, it's pretty obvious they think it's impossible to fire teachers with tenure. It isn't. I'll listen to small, precise tweaks, but "killing tenure," to me, simply forces us to ask: And replace it with what?
You want teachers to be just as insecure in their future as doctors and lawyers, who people keep wanting to compare teachers to in order to show how important they think teachers are? Well then, you have got to pay teachers like doctors and lawyers, and you've got to put enough infrastructure in place so that the people evaluating teachers aren't completely overwhelmed with their job.
I can't emphasize this enough: Tenure exists because it's a cheap solution compared to what it would otherwise cost to achieve the same quality of product. You're getting people to agree to smaller salary in exchange for security. It's a strategy.
if you are willing to pay much more for education than you are now in order to fix this and end tenure, cool. But before you do that, consider: Do you have any idea how cutback schools are right now? It's not like we've tried throwing money at the current problem, and it's failed. It's never been tried, period.
As I say this, I understand it's not that schools are cheap. Costs are rising for a variety of reasons that have nothing to do with unions, and the "cost" of the union is skyrocketing because of the far bigger problem of American health care, but schools themselves are operating with a level of "no, you can't replace that," "no, you can't keep using that," that none of the techies in Silicon Valley can begin to fathom. If they didn't have to do that, there'd be clear benefits.