Earlier this month in New Zealand, the minister of education Hekia Parata shared a piece of knowledge that has become common the world over. In the Southland Times, “Experts have found that four consecutive years of quality teaching eliminated any trace of socio-economic disadvantage.”

The source of this is an American economist by the name of Eric Hanushek, a professor at Stanford University, who has been spreading this for the past several years. According to Hanushek, “Good teachers are ones who get large gains in student achievement for their classes; bad teachers are just the opposite.”

He looks at the distribution of student test scores, and imagines that if we could fire the teachers who are associated with the lowest 10% or so, then we would make huge gains. This is the theory behind a great deal of the push for 21st century K-12 education reform in the US. In order to identify and efficiently dispatch these slackers, we need national standards, and rigorous tests aligned to them.

This has led reformers to advocate that we:

Test students more often, so we can measure learning incrementally. Test students in every subject, and at every grade level—even kindergarten, so that all teachers can be properly judged.

Eliminate barriers to firing the “bad teachers” who get low scores, so due process and seniority protections have to go.

Create new evaluation plans that give significant weight to “value added” measures drawn from test scores, for both teachers and administrators.

Hanushek has also argued, by the way, that more money won’t help schools succeed, nor will small class size. The teacher is the only variable worth targeting. Unions are a problem to the extent to which they make it difficult to quickly fire teachers identified as ineffective.

But the real world is proving to be a difficult place for Hanushek’s theories to be verified. No school has ever replicated the results predicted by his “four great teachers in a row” theory. In fact, there is no real research to support the idea that we can improve student achievement this way—it is all based on extrapolations.

And in fact, new data shows that in the three large urban school districts where these reforms have been given full rein, the results are actually worse (pdf) than in comparable districts that have not gone this route.

Some of the key findings from the Economic Policy Institute’s April report:

Test scores increased less, and achievement gaps grew more, in “reform” cities than in other urban districts.

Test-based accountability prompted churn that thinned the ranks of experienced teachers, but not necessarily bad teachers.

School closures did not send students to better schools or save school districts money.

Most importantly:

The reforms missed a critical factor driving achievement gaps: the influence of poverty on academic performance.

This last point is crucial. This attention to the supposedly pivotal role teachers play in student success comes at a time when the number of children in poverty has been on the rise. According to a study in 2011 (pdf), one school in five was considered high poverty, up from one in eight in the year 2000. Another study showed that “many high-poverty schools receive less than their fair share of state and local funding… leav(ing) students in high-poverty schools with fewer resources than schools attended by their wealthier peers.”

While conservative economists such as Hanushek wish to focus our attention on “bad teachers,” in actuality by far the largest factor affecting school performance is family income. In fact, the achievement gap between rich and poor has grown to be twice as large as the black/white performance gap in America.

Teachers are important, and of course we want to recruit the most expert and brightest possible, and give them lots of support. But the expansion of tests, and efforts to make teacher jobs depend on ever-rising scores, are turning our schools into test preparation factories.

Hanushek’s ideas have been driving a vast school reform project, which has been underwritten by the largest philanthropies on earth—starting with the Gates and Walton foundations. Now that this project is a decade old, and showing little signs of success, the time has come for a major reappraisal.

Rather than vesting our trust in tests to identify and weed out the worst teachers, why not invest some confidence in these teachers themselves, and empower them to engage in peer observation and growth through proven programs like Peer Assistance and Review? These programs feature experienced teacher coaches working with peers who have been identified as struggling. This has been found to be an effective way to strengthen teachers—and remove those who are unable to improve.

And how about some direct action to reduce the extreme income gap between wealthy and poor? An increase in the minimum wage would provide increased stability to millions of families, which would help children focus on their studies instead of where their next meal will come from. Most schools have cut nurses, librarians and counselors, at the same time we are expanding our investment in measurement systems.

So I offer this warning to the people down under and beyond. This misguided emphasis is no more likely to work there than it has in the US—unless of course, New Zealand truly is “opposite land,” where hot snow falls up.