Merit pay didn't raise the test scores of students in Nashville, Tenn., during a three-year period when it was tried in an experiment that ended in 2009. This is the story beneath a raft of "Merit Pay Doesn't Work" headlines attached to news reports around the country this week describing a new study about the limited experiment.

The Grand Rapids Press provides a bit more nuance: "Study Shows Merit Pay 'No Silver Bullet' to School Reform." That's true enough, and in the accompanying story reporter Dave Murray fairly highlights the key implications of the study. In Education Week, Rick Hess of the American Enterprise Institute points out that the study doesn't tell us anything about how to improve the teaching profession as a whole. And as Jay Greene of the University of Arkansas Education Reform Department observes, it's no surprise that one isolated market-based plan failed to significantly impact a heavily monopolized system like government-run schooling.

Not surprisingly, school employee unions are shouting the racier headlines from the roof tops. That's because the American Federation of Teachers and the National Education Association prefer to see teachers paid like 20th century assembly line workers rather than as professionals, pretending that all are equal (and thus interchangeable) regardless of performance. The union contracts' "single salary schedule," plus life-long tenure provisions and the "golden handcuffs" of defined-benefit pensions programs, ensures that teachers only get rewarded for racking up ever more years on the job.

To reinforce their weak arguments, the unions often make logically fallacious appeals to tradition (even comparing the single salary schedule to "Mom and apple pie"). They do so largely because there's no good evidence showing that teachers obtaining additional pedagogy degrees or piling up more seniority impacts student achievement in any positive way. As this recent study suggests, the case for merit pay isn't iron-clad, either. Still, merit pay and other differential pay structures are improvements over the single salary schedule model used by nearly every public school in the country.

A single salary schedule rewards teacher inputs while demanding that schools ignore student  outputs when determining pay. A merit pay system focuses first on performance, and de-emphasizes (but does not necessarily eliminate) inputs. This realignment is a vital step to reforming the public school system. It's why the Mackinac Center sketched out how a privately financed merit pay pilot program could work.

Schools that do focus on outputs are having tremendous success. For example, Harlem Village Academies, a public charter school in New York City, does not treat all of its teachers the same. Instead, teachers are encouraged to become autonomous, take risks, and be creative. They have the freedom to choose their own textbooks and design their own courses, but — and here's the key — they're then held strictly accountable for performance. The outcomes so far are outstanding.

Deborah Kenny, the CEO of Harlem Village Academies, explained in the Wall Street Journal why she chose to break from the traditional mold and manage teachers differently: "We need to stop treating teachers like industrial-era workers and start treating them like professionals."