Their futures are in his hands. Photographer: Robert MacPherson/AFP/Getty Images
Their futures are in his hands. Photographer: Robert MacPherson/AFP/Getty Images

U.S. schools don't have enough great teachers. There are various reasons for that, chief among them tenure protections that prevent principals from cutting loose low performers and union contracts that require the worst teachers to be paid the same as the best. But the trouble begins even before teachers arrive in the classroom: Education schools at U.S. universities don't give them the preparation they need to succeed.

Secretary of Education Arne Duncan wants to change that. Last week, he said he would draft new regulations to make federal aid to education schools contingent on the performance of their graduates. Duncan's crusade against ineffective teacher curriculums is admirable. Unfortunately, the proposed measuring standards won't begin to get to the root of what has been a national scandal for decades.

Effective teachers can make a significant difference in a child’s achievement level and career trajectory. One study even found that replacing a low-performing teacher with an average teacher raises a student’s lifetime career earnings by $250,000.

But states are still figuring out the best ways to measure the impact that teachers have on student achievement -- an idea known as “value added.” And questions abound about whether such measurements, which are based on standardized tests, can be made accurately. The American Statistical Association recently released a cautionary statement about over-reliance on value-added metrics. And even if the metrics were foolproof, most teachers cover areas or grade levels that aren't subject to standardized tests.

Duncan has indicated that value-added metrics will be part of the new regulations, which are already drawing attacks from critics who helped kill a previous Barack Obama administration effort to hold teacher-training schools accountable. While other metrics that the department seems to be considering aren't controversial, they aren't of much use, either.

For instance: Knowing the percentage of graduates who land teaching jobs is helpful information for potential applicants, but it doesn't say much about a program’s quality. Also of limited value is the length of time that graduates remain in the teaching profession. Length of service and mediocrity can go hand in hand in a system where it's hard to fire anyone and where seniority, rather than merit, is rewarded.

The best step may be the simplest: Reward education schools that enroll high percentages of high-performing students. According to a recent study by the National Council on Teacher Quality, only 1 in 4 education schools restrict admission to the upper half of college students. A 2007 McKinsey study found that, globally, countries with the highest-performing school systems recruit teachers only from the top third of their classes. In South Korea, only the top 5 percent of students are recruited for a career in teaching; it’s the top 10 percent in Finland. In the U.S., most programs don't even require a minimum grade-point average.

The National Council on Teacher Quality study also found that 8 of 9 elementary-education programs, and 2 of 3 secondary-education programs, are failing to prepare their students for the new Common Core curriculum. And 9 of 10 programs fail to guarantee that their students are placed with effective teachers as part of their training.

A new federal evaluation system should reward schools that correct these flaws and punish those that don’t. Even if it does this, addressing the country’s need for more good teachers will require a more comprehensive approach, one that cracks open tenure protections and ends lockstep pay scales. Raising professional standards will send universities a message: Quit cranking out education-school graduates who won't make the grade.

To contact the senior editor responsible for Bloomberg View's editorials: David Shipley at davidshipley@bloomberg.net.