“Union teacher” isn’t the distinction, as unions also provide useful professional insurance even in states where they do practically nothing when it comes to employer/employee relations, so many teachers are still members. Do states with strong teachers unions have lower firing rates than those where the unions do almost nothing? I’m saying we may have to look elsewhere for the explanation, if the firing rate in states with nearly-useless teachers unions aren’t closer to where you think they should be.

I’d guess the rates remain low even with weak unions because schools are piss-pants scared of bad publicity, due to the public’s role in (indirectly) hiring and firing the top of their pyramid, and in allocating funding. But maybe I’m wrong and rates of firing are closer to whatever you consider a desirable rate, in states with weak unions. I did go looking, but couldn’t find datasets tackling that in particular. Frustrating, because with that we could get at least a strong hint of the actual effect of unions on this specific thing.