Is it actually that hard to fire teachers? The numbers I can find indicate that, depending on the state, around 3-5% of "tenured" teachers are fired every year. That's definitely a higher for-cause termination rate than anywhere I've worked. It's also higher than in many of the countries that have good school systems.

I'm not exactly sure what the solution is, but I don't think simply firing teachers will do much. Even firing teachers and raising pay, while both are probably necessary (if you're offering $30k/year, don't be surprised that you get $30k/year types of applicants), doesn't solve the worst problems. Some schools are just a mess of poor discipline that's hard to get a handle on; you could have strict performance reviews and pay $70k/year and I think there are schools that will still be difficult to fix.

One particular problem with giving administrators more authority to fire people is that I have this sneaking suspicion that they'll actually fire the best teachers! The best teachers I had in high school were mostly not very popular with the administration, because they deviated a bit from the official line and were actually effective at teaching, instead of treating the entire class as year-long prep for a multiple-choice test, Kaplan-style. Principals and superintendents are by and large like a less competent version of your stereotypical corporate middle-management, rotating in and out of schools and districts in 2-4 years, changing policies arbitrarily to leave their mark on things and not staying around to see them through, all aimed at moving up the ranks. Anything that gives them more power without first greatly reforming that system is bad imo.