But improving the quality of teachers who work with poor kids seems more about insufficient inflow of the talented than insufficient outflow of the untalented. One study, based on a policy change in Chicago, found that even when dismissal rules are relaxed, many principals still choose not to fire anyone — including at the worst-performing schools — perhaps at least partly because of the challenge of finding decent replacements.

Weakening job security in the absence of other reforms may even discourage good people from entering or sticking with the profession.

That’s because job security is one of the key forms of compensation that we still offer to educators as their salaries have gotten less competitive over time, thanks to a pesky combination of women’s lib and stingy taxpayers.