Stanford’s Eric Hanushek reports on research he's done into teacher effectiveness:
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.
These aren't just superstars that Hanushek is talking about, either. About 16% of teachers are one standard deviation above the mean, so these are good teachers but not necessarily sensational ones. Karl Smith is impressed:
Social value isn’t a feel good concept. Hanushek limits himself to future earnings of the students. The other big drivers are always crime reduction and public assistance reduction. So we are saying better teachers lead to higher wages, lower crime and less welfare. This is a far cry from trying to put numbers on soft factors like civic engagement.
I do wish that someone would connect the dots and make the obvious yet important point that Rick Hess has been making for ages: shrinking class sizes over the last forty years has diluted the teacher talent pool. Had we stayed at the teacher-student ratios of the 1970s, we’d have 2.2 million public school teachers rather than 3.2 million. Know what else happened over the last 40 years? Labor market discrimination against women and African Americans declined, giving talented female and African American workers who had once gravitated to the teaching profession other options. Allowing effective teachers to take on larger classes in exchange for more pay could have a powerful positive effect. With the same compensation bill, we could pay far higher salaries.
It makes sense that we'd be paying teachers more if there were fewer of them, though I'm not sure that's how things would actually play out in the real world. However, given the lack of evidence that lower class sizes improve educational outcomes, it seems worth a try.
Still, this leaves us with the biggest question unanswered. I think lots of people are sympathetic to the idea that good teachers make a big difference, but how do we decide who the good teachers are? Or who the best teaching recruits are? Value-added results from standardized testing regimes seem to be about the best we have at the moment, and those are pretty questionable. But for a wide variety of reasons both good and bad, there's no way that we'll ever end up dedicating large sums of money to a massive social experiment in teacher selection and retention unless we're pretty sure we have this question licked.
Obviously there are plenty of other problems bedeviling education too: concentrated poverty, disaffected parents, pedagogical conflicts, etc. etc. But teacher quality comes up repeatedly, and the problem of how to actually judge teacher quality in the real world always comes up right along with it. I'm not sure what the answer is. Lots of experimentation, I suppose.