Good teachers matter. This may seem obvious to anyone who has a child in school or, for that matter, to anyone who has been a child in school. For a long time, though, researchers couldn't actually prove that teaching talent was important. But new research finally shows that teacher quality is a close cousin to student achievement: A great teacher can cram one-and-a-half grades' worth of learning into a single year, while laggards are lucky to accomplish half that much. Parents and kids, it seems, have been right all along to care whether they were assigned to Mrs. Smith or Mr. Brown.

　　Yet, while we know now that better teachers are critical, flaws in the way that administrators select and retain them mean that schools don't always hire the best.

　　Many ingredients for good teaching are difficult to ascertain in advance—charisma and diligence come to mind—but research shows a teacher's own ability on standardized tests reliably predicts good performance in the classroom. You would think, then, that top-scoring teachers would be swimming in job offers, right? Not so, says Vanderbilt University professor Dale Ballou. High-scoring teaching applicants "do not fare better than others in the job market," he writes. "Indeed, remarkably they do somewhat worse."

　　Even more surprising, given the national shortage of highly skilled math and science teachers, school administrators are more keen to hire education majors than applicants who have math or science degrees. No one knows for sure why those who hire teachers routinely overlook top talent. Perhaps they wrongly think that the qualifications they shun make little difference for students. Also, administrators are probably naturally drawn to teachers who remind them of themselves.

　　But failing to recognize the qualities that make teachers truly effective (and to construct incentives to attract and retain more of these top performers) has serious consequences. For example, because schools don't always hire the best applicants, across-the-board salary increases cannot improve teacher quality much, and may even worsen it. That's because higher salaries draw more weak as well as strong applicants into teaching—applicants the current hiring system can't adequately screen. Unless administrators have incentives to hire the best teachers available, it's pointless to give them a larger group to choose from.

　　If public school hiring processes are bad, their compensation policies are worse. Most districts pay solely based on years of experience and the presence of a master's degree, a formula that makes the Federal General Schedule—which governs pay for U.S. bureaucrats—look flexible. Study after study has shown that teachers with master's degrees are no better than those without. Job experience does matter, but only for the first few years, according to research by Hoover Institution's Eric A. Hanushek. A teacher with 15 years of experience is no more effective, on average, than a teacher with five years of experience, but which one do you think is paid more?

　　This toxic combination of rigid pay and steep rewards for seniority causes average quality to decline rather than increase as teacher groups get older. Top performers often leave the field early for industries that reward their excellence. Mediocre teachers, on the other hand, are soon overcompensated by seniority pay. And because they are paid more than their skills command elsewhere, these less-capable pedagogues settle in to provide many years of ineffectual instruction.

　　So how can we separate the wheat from the chaff in the teaching profession? To make American schools competitive, we must rethink seniority pay, the value of master's degrees, and the notion that a teacher can teach everything equally well—especially math and science—without appropriate preparation in the subject.

　　Our current education system is unlikely to accomplish this dramatic rethinking. Imagine, for a moment, that American cars had been free in recent decades, while Toyotas and Hondas sold at full price. We'd probably be driving Falcons and Corvairs today. Free public education suffers from a lack of competition in just this way. So while industries from aerospace to drugs have transformed themselves in order to compete, public schooling has stagnated.

　　School choice could spark the kind of reformation this industry needs by motivating administrators to hire the best and adopt new strategies to keep top teachers in the classroom. The lesson that good teachers matter should be taught, not as a theory, but as a practice.