The Republican presidential debates have been replete with discussions about our economic future, but to listen to the candidates you’d think that the biggest problem is an onerous U.S. tax code.

I’m all for sensible tax reform, but prosperity depends far more on our skill base than on cutting tax rates that are already low by international standards. If the Republicans want to battle for a more prosperous, and stronger, country, they must start spending a lot more time fighting the failures of American education.

The attached figure shows the correlation between the logarithm per-capita income levels in 2010 and math PISA test scores in 2009. The Organization for Economic Cooperation and Development’s Program for International Student Assessment, known as PISA, tests 15-year-olds in a range of generally prosperous countries, and takes on values from 200 to 800 (similar to the math SAT). Tests are also given for reading and science ― the scores are quite closely correlated across subject area ― but the math results are the best predictor of incomes across countries. I excluded Luxembourg and Lichtenstein because of size, and subnational Chinese areas, such as Hong Kong and Shanghai.

The graph illustrates that a 46-point test score increase, which is about 10 percent of the average score across countries, is associated with an increase of more than 90 percent in country level incomes. The test score variable can explain, in a statistical sense, the lion’s share of income differences across these countries.

Although it’s sensible to be a bit skeptical about figures like this, there is a long and distinguished literature linking education with economic outcomes at the individual, country and metropolitan area level. Economists have found that earnings rise with education even among identical twins and that randomly getting a better kindergarten teacher produces higher adult earnings.

At the metropolitan level, education predicts earnings growth, not just income levels, and the presence of a land-grant college prior to 1940 is a strong predictor of economic success today.

At the national scale, fears of reverse causality are allayed by the fact that education predicts improvements in income and government quality, but ameliorations in those areas don’t predict improvements in education.

All in all, the link between education and prosperity is about as solid as anything in the social sciences.

By contrast, the statistical link between tax rates and prosperity is far weaker. Across countries, incomes are typically higher where governments spend more, as a share of gross domestic product. This is known as Wagner’s Law, and it doesn’t mean that big government increases prosperity, because government spending is primarily reflecting, not causing, high incomes.

But empirical studies, compromised by a host of tricky statistical issues, have typically found a murky relationship between government size and economic growth. U.S. tax cuts also typically appear to have modest impacts on economic activity.

This may not be surprising because our tax rates are already low relative to world standards.

I agree with Republican leaders who want to make the government more efficient and reduce our tax burden, but lower taxes mean less spending, and this is far from a silver bullet for the economy.

Similarly, the U.S.’s economic problems don’t primarily reflect deficient infrastructure or too expensive energy or the actions of the Environmental Protection Agency.

I support smart reform in all these areas, but if we fail to address the primary issue ― our skill deficit ― we’re fiddling while the country declines. Indeed, the figure shows that U.S. wages are already high relative to our skill levels. The big challenge is to ensure that Americans have the tools to thrive in an information age.

Our current PISA math scores put us in the middle of the pack. We’re on a par with Portugal, ahead of Italy and Azerbaijan, and behind Hungary and Slovenia. We’re far behind countries such as South Korea and Singapore.

Why should we expect an American with limited skills to earn dramatically more than an equally skilled counterpart in China or India? An American consultant doesn’t expect to earn a wage premium for advising an Indian company just because she’s from the U.S.

People who sell their time through the online marketplace Amazon Mechanical Turk can’t expect to earn more because of their location. Place matters ― we’re still educated by the people around us. The importance of having smart neighbors explains why cities like Seattle, Minneapolis and Boston continue to thrive.

But proximity is worth less and less if you aren’t learning from the people around you. Once upon a time, Americans could expect to earn more than equivalently skilled Asians or Europeans, because of our natural resources and a government that was exceptional in its stability, rule-of-law and embrace of capitalism.

Today, there are plenty of countries where entrepreneurs can thrive.

The would-be Republican candidates all champion enduring American greatness, but how can that greatness persist unless the U.S. is one of the most skilled countries on the planet? The 20th century was America’s century in part because we were so well educated.

The Republican Party’s leaders should fight for better schools, because they have plenty to add to the education debate. The most remarkable education success stories of the past decade have been charter schools that expose their students to long classroom hours.

That message should be a perfect fit for Republicans ― the U.S. becomes smarter through competition and hard work. Years of research have taught us that teacher quality is paramount; this, too, can be a Republican issue. Candidates should fight to ensure enough school competition so that excellent teachers get top salaries and mediocre teachers get fired.

Republicans should also embrace the promise of new teaching technologies, such as New York’s School of One, which uses computers to personalize lessons. Republican candidates should offer an optimistic vision of a stronger and fairer country built on skills and entrepreneurship.

Yet some of these politicians seem to think that everything will be fine as long as Washington abandons its push to improve education. This is a path to mediocrity.

As Margaret Spellings, who served as secretary of education under President George W. Bush and is my colleague on the Bill and Melinda Gates Foundation United States Program Advisory Panel, told the New York Times, “We tried that for 40 years,” and “the results were far from stellar.”

Washington needs to be involved to ensure localities don’t put unions ahead of children. Massachusetts lifted its unfortunate cap on charter schools partially because of the pressure created by the Race to the Top program. A Republican policy could be even more effective.

Indeed, Republican presidents have a proud legacy of making the U.S. stronger through education. Abraham Lincoln signed the 1862 Morrill Act establishing land-grant colleges (which his Democratic predecessor had vetoed).

Dwight D. Eisenhower supported the Sputnik-era efforts that brought more science into schools. During the Ronald Reagan administration, the “Nation at Risk” report led to a national focus on science and math that created big returns for disadvantaged youths. Bush wanted to be an education president with the No Child Left Behind law.

Americans will earn what our talents produce. Any Republican or Democrat who wants to repower our economy must recognize that the nation’s future depends on its human capital, far more than infrastructure or energy or finagling with the tax code. 

By Edward Glaeser

Edward Glaeser, an economics professor at Harvard University, is a Bloomberg View columnist. He is the author of “Triumph of the City.” The opinions expressed are his own. ― Ed.

(Bloomberg)