Americans are under the misapprehension that all of their school woes stem from poor teachers. But even in poor districts like the one my spouse teaches in, which have accumulated a whole layer of apathetic teachers, the impact of both poor and excellent teachers is way overestimated, and the impact of poor and excellent administrations (both the school principal and the district leadership) is tremendously underestimated. A good principal, particularly one with strong school board backing, can almost single-handedly turn an entire school around (I've seen this happen twice now). An excellent teacher with a poor principal and negligent school board can do very little other than provide a strong role model for the most promising students, and (with great effort) pull a handful more of failing students up to the barely passing level than their less talented peers.
Primarily, good principals act just like good engineer managers in corporations. Just as good managers keep engineers isolated from the bullshit of upper management and adjacent managers, and give good engineers space to do their jobs, so do good principals let their good teachers do their job, and intervene when poor teachers fail to meet expectations.
Regarding the other factors mentioned, I do think poverty is a major hurdle, and the author of this piece rightly underlines its importance in poor school performance, but poverty is primarily an issue in that high-levels of poverty correlate strongly with lack of parental support and engagement (and not always due to a lack of care; often it's because these are single-parent households where that one parent is working all the time). But here an excellent principal can also make a major impact by rallying formerly disengaged parents around their kids and their kids' teachers, and supporting single-parent households where the parent is working multiple jobs.
It makes me sad to see all this rhetoric around teachers in the U.S., not only because it's depressing for my spouse to be so unappreciated by people outside the teaching profession, but also because I know it will do little to fix the main problem: school poor administrations. Nor will it address any of the other major contributing factors, like poverty and the lack of respect in high school academic excellent so prevalent in our culture, rich and poor alike.