Greg Mankiw's Blog: The Value of Good TeachersThere is a lot of dislike in the educational establishment for programs like Teach for America and Alliance for Catholic Education, much of which is justified and some of which I think is bitterness insiders always feel for those who bypass credentialist regimes.
From Eric Hanushek:
A teacher one standard deviation above the mean effectiveness annually generates marginal gains of over $400,000 in present value of student future earnings with a class size of 20 and proportionately higher with larger class sizes. Alternatively, replacing the bottom 5-8 percent of teachers with average teachers could move the U.S. near the top of international math and science rankings with a present value of $100 trillion."
Some of what frustrates me about such discussions is that it is too often framed as "Are these untrained college kids good teachers?" where goodness is measured on some absolute scale and not "How good are they compared to the marginal teacher?" Are they better than the alternatives -- the credentialed person who is displaced or leaving the position vacant?
If the bottom 5-8% of teachers are as bad as Hanushek says then it becomes a little more likely that a slightly above average college graduate without training is better at the margin.
(Although I suppose that is only true if the hiring process of the school for the "regular" teachers is somewhat efficient. If they hire completely randomly then the TFA or ACE kid is as likely to be displacing one of the over performing teachers as an under performing one, which makes TFA & ACE worse. But if that's the case, we have a lot bigger problems than TFA and ACE.)
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Adam Ozmiek is right on:
There are really two important claims here. I think progressives tend to be very pleased with claims like the first one, which is that teachers have a very high value. You can find similar results in the work of Raj Chetty, which suggests that good kindergarten teachers are worth $320,000. If this is true then the marginal benefit of teaching skill -or quality, if you want to think of it that way- is far below the marginal cost, and therefore we should increase wages to draw more talented teachers.I would tweak the end of each of those paragraphs a bit. Rather than increasing wages to draw more talented teachers, I would shift the focus to increasing pay for talented teachers. How we determine who is talented is of course a thorny issue.
However, the second claim is just as important and is suggested by, although not a necessary condition of, the first: if good teachers are very valuable, then bad teachers are very costly. This means we should be willing to pay more for good teachers, but it also increases the benefit of getting rid of bad teachers and ensuring we have a system that can do that. After all, every dollar spent on a bad teacher has the high opportunity cost of good teachers.
I would also expand on the last sentence of the latter 'graph. The cost of bad teachers is not only the opportunity cost of their salaries, but the opportunity cost of the man-hours students must spend with them. I would put more stress on that than the salaries. Those are hours students do not get back, and since the number of hours you spend in primary and secondary education is fixed, you're directly displacing hours spent with good or even average teachers.
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I don't feel like searching for the research now, but I recall seeing that once you get class size under a certain threshold (in the upper 20's I believe) the impact of class size is near negligible. I conclude from this that you might not only be better off firing the bottom 5% of teachers and replacing them with a teacher with an average expected value, but you may also be better off firing them and not replacing them at all. 100 teachers -- including 5 from the far left tail of the distribution -- with 20 kids each may very well be worse than 95 teachers with 21 kids each.
It's a hypothesis worth investigating anyway.
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Contrast Hanushek's observation with two bullet points from my Waiting for Superman review:
• I posted a couple of weeks ago this stat from the movie, which remains shocking:Those bottom five to eight percent are not being culled despite their destructivity.
About one of 57 medical doctors and one of 97 lawyers loses his or her license annually for malpractice. In contrast, only one in 2,500 unionized, public school teachers with tenure gets fired each year.• A similar stat also stood out. I don't recall the exact figures, but of the several hundred school districts in Illinois, only 60 or so have ever attempted to fire a single tenured teacher, and of those only half have succeeded. That is absurd. There is no organization in the world that can hire tens of thousands of people without making a mistake and ending up with someone who is not right for the job. You can't run an organization if you assume that once someone has made the decision to hire X, that decision can never be revisited or reevaluated.
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Hanushek has been interviewed by Russ Roberts for EconTalk several times. He is worth listening to.