During the first 70 years of the 20th century, inequality declined and Americans prospered

together. Over the last 30 years, by contrast, the United States developed the most unequal distribution of income and wages of any high-income country.

Some analysts see the gulf between the rich and the rest as an incentive for strivers, or as just the way things are. Others see it as having a corrosive effect on people's faith in the markets and democracy. Still others contend that economic polarization is a root cause of America's political polarization. Could, and should, something be done？

Claudia Goldin and Lawrence F. Katz, two Harvard economists, think yes. Their book, the Race Between Education and Technology (Harvard, $ 39.95), contain many tables, a few equations and a powerfully told story about how and why the United States became the world's richest nation--namely, thanks to its schools.

The authors skillfully demonstrate that for more than a century, and at a steady rate, technological breakthroughs--the mass production system, electricity, computers--have been increasing the demand for ever more educated workers. And, they show, America's school system met this demand, not with a national policy, but in grassroots fashion, as communities taxed themselves and built schools and colleges.

If only it were that easy.

The authors' argument is really two books in one. One offers an incisive history of American education, especially the spread of the public high school and the state university system. It proves to be an uplifting tale of public commitment and open access. The authors remind us that the United States long remained "the best poor man's country". A place where talent could rise.

The other story rigorously measures the impact of education on income. The authors' compilation of hard data on educational attainment according to when people were bona is an awesome achievement, though not always a gripping read.

They show that by the 1850s, America's school enrollment rate already "exceeded that of any other nation". And this lead held for a long time. By 1960, some 70 percent of Americans graduated from high school--far above the rate in any other country. College graduation rates also rose.

In the marketplace, such educational attainment was extremely valuable, but it didn't produce wide economic disparity so long as more people were coming to the job market with education. The Wage premium-- or differential paid to people with a high school or a college education--fell between 1915 and 1950.

But more recently, high school graduation rates flatlined at around 70 percent. American college attendance roses, though college graduation rates languished. The upshot is that while the average college graduates in 1970 earned 45 percent more than high school graduates, the differential three decades later exceeds 80 percent.

"In the first half of the century," the authors summarize, "education raced of technology, but later in the century technology raced ahead of educational gains."

Proving that the demand for and supply of educated workers began not in the time of Bill Gates but in the era of Thomas Edison is virtuoso social science. But wasn't a slowdown in rising educational attainment unavoidable？ After all, it's one thing to increase the average years of schooling by leaps and bounds when most people start near zero, but quite another when national average is already high.

The authors reject the idea that the United States has reached some natural limit in educational advances. Other countries are now at higher levels.

What, then, is holding American youth back？

The authors give a two-part answer. For one thing, the financial aid system is a maze. More important, many people with high school diplomas are not ready for college.

The second problem, the authors write, is concen

A．The wage movements in the U.S. are dominated by swings in the demand for education-related skills.

B．The American educational system is what made American the richest nation in the world.

C．Technology raced ahead of education in the first half of the 20th century.

D．American high school graduation rates leveled off at 80 percent in 1970.