Students in high-poverty schools have yet another factor working against them: their worst teachers are actually the worst of the worst.

According to a CALDER working paper, the least effective teachers in high-poverty schools are considerably less effective than the least effective teachers in low-poverty schools.

Interestingly, there isn't much difference in effectiveness between the highest performing teachers in the same schools, and teachers overall aren't necessarily less effective in high-poverty schools compared to low-poverty schools. There's only measurable variation in the bottom tier of teachers, with ineffective teachers in high-poverty schools doing more damage than their counterparts at the low-poverty schools.

Why? The authors think it's all due to how veteran teachers respond to their surroundings. Teachers in low-poverty schools have a more "doable job" and are generally surrounded by fairly capable colleagues, while more senior teachers in high-poverty schools may fall victim to stress and burnout. The solution, of course, involves incentives to keep high performing teachers serving longer in such schools.

There's also food for thought here for those who think school-wide measures are better than individual measures when it comes to rewarding teachers for great performance or holding the weakest teachers accountable. School-wide measures may disproportionately disadvantage high-performing teachers in high-needs schools, while also making the lower performers look a lot better than they actually are.