Quarterbacks in the NFL are extremely hard to draft because the best college quarterbacks play a spread offense. A spread offense makes it easy to "read" a defense, but can never work in the NFL where defenders are too fast and athletic for there to be that much space within an offensive line. So, it's impossible to predict how well a college quarterback will actually perform in the NFL.
Teaching faces a similar problem. Degrees and certifications are not good predictors of performance. What matters is classroom skills. And the only place to gauge those is in a real classroom. And yet the payoff of having a good teacher is huge:
students of a very bad teacher will learn, on average, half a year’s worth of material in one school year. The students in the class of a very good teacher will learn a year and a half’s worth of material. That difference amounts to a year’s worth of learning in a single year. Teacher effects dwarf school effects: your child is actually better off in a “bad” school with an excellent teacher than in an excellent school with a bad teacher. Teacher effects are also much stronger than class-size effects. You’d have to cut the average class almost in half to get the same boost that you’d get if you switched from an average teacher to a teacher in the eighty-fifth percentile. And remember that a good teacher costs as much as an average one, whereas halving class size would require that you build twice as many classrooms and hire twice as many teachers.
The financial advisor industry also faces the same problem. But they have the money to simply lower the bar, vacuum up every willing brain and actually try them on the job. A company might hire fifty candidates, spend $250,000 on each and then let forty of them go in a couple of years if they fail to drum up and maintain enough clients.
I can attest to the general workability of this approach in teaching. I teach corporate workshops on technology-related topics. The company I teach through for operates on a philosophy similar to financial advisors. Even the ratios are the same -- for every five candidates it trains, only one is still teaching for the company two years later. The client corporations and students provide evaluations of instructors and course materials -- these are then used to "manage by numbers" and weed out unsuccessful instructors and authors. Over time, they've found that bad instructors are those with poor classroom skills. These instructors often know the stuff, but can not teach it. Mainly because they have no control of the classroom and fail to personalize instruction to what students are actually learning.
And from the other side, I see the effect of my children's teachers on them. It constantly surprises me how little personal interaction there is between the teachers and the kids. Often, S1 comes home hazy on some material that used an unfamiliar word. Explaining it to him often takes as little as a minute, but it's a minute that his teacher in school never realized that he needed. That lack of awareness, from my corporate teaching experience, is a sure indicator of a poor teacher.
There are policy suggestions in the article, about teacher tenure and the rest. But the most important insight is that we (as a society) need to be willing to hire anyone willing to be a teacher, give them basic instruction on pedagogy and then evaluate them on how well they actually do. Like a quarterback, like a financial advisor, the best teachers are those who can teach. And there is no way to find out unless you cast a net far and wide and are willing to fire 80% of the new candidates that come in. And, of course, pay the 20% who make it the way we pay our successful quarterbacks and financial advisors i.e. top rate.