MUCH of today's debate about immigration revolves around the same old questions: How much do immigrants contribute to production? Do they take jobs away from people born in the United States? And what kinds of social services do they use? Yet every immigrant represents much more than just one worker or one potential citizen. To understand fully how immigration will shape the economy, you can't just look at one generation — you have to look into the future.

Sociologists and economists are just beginning to study the performance of second- and third-generation members of immigrant families. Because of the variety of experiences of people from different countries and cultures, it's not easy to generalize. But recent research has already uncovered some pertinent facts.

Education is a good place to start, because it's strongly correlated with future earnings. Children of immigrants complete more years of education than their native-born counterparts of similar socioeconomic backgrounds. "You can expect a child of immigrants whose parents have 10 years of education to do a lot better than a child of natives whose parents have 10 years of education," said David Card, a professor of economics at the University of California, Berkeley. Being a child of immigrants, he said, "sort of boosts your drive."

As a whole, though, the second generation also tends to move toward the American average, Professor Card said. Some graduate from high school even though their parents didn't, but some whose parents have doctorates will earn only bachelor's degrees. Still, it can take several generations for poor immigrant families to catch up to American norms. "For the largest immigrant group — that is Mexicans and Mexican-Americans — the picture is progress, but still lagging behind other Americans," said Hans P. Johnson, a research fellow at the Public Policy Institute of California. "They're doing much better than their parents, graduating from high school, but they still have very low graduation rates from college."

But despite the lag in education, Mr. Johnson said, Mexican immigrants and their families don't have much trouble finding jobs. "One of the paradoxes of Mexican immigration is that you have these workers with low skills but incredibly high employment rates," he said. "The second generation isn't able to maintain employment levels that are quite so high, but they're basically in the same ballpark."

Second generations of immigrant families are managing to climb the skills ladder, too. A recent survey by the Census Bureau reveals that 40 percent of the female workers and 37 percent of the male workers in the second generation took professional or management positions, up from 30 and 24 percent, respectively, in the first generation. The survey, taken in 2004, included many adults whose parents came to the United States decades ago, noted William H. Frey, a visiting fellow at the Brookings Institution in Washington who compiled data from the survey. With more recent immigrants, he said, it's possible that lower education rates may eventually lead to worse outcomes.

Other factors could also make success more difficult for today's children of immigrants, compared with those of the past.

One is increased competition. The children of Italians and Poles who came to the United States around the turn of the 20th century didn't face much of it, because the government imposed quotas on immigration after their parents arrived, said Roger Waldinger, a professor of sociology at the University of California, Los Angeles. By contrast, the children of recent arrivals face competition from successive waves of immigrants from numerous regions.

Inequality of income and wealth is another factor that could affect opportunities. "The second generation of Italians and Poles came of age in an era of historically low inequality," Professor Waldinger said. "The second generation of Mexican immigrants is coming of age in an era of historically high inequality, and that has to work to the disadvantage of those with low levels of schooling."

But there are also forces working in the opposite direction. For one thing, the children of today's immigrants will have much better access to education and the labor market than those of a century ago. "It almost certainly will be the case that tomorrow's third generation will have better outcomes than today's third generation," Mr. Johnson said. "The conditions today are better in terms of educational opportunities."

Adding to that, members of several immigrant groups have often risen quickly to — or even started at — the top of the wage scale. Professor Waldinger said that "the median for Indian immigrants is 16 years of schooling" and that, on balance, "the Indians, the Koreans, the Chinese — they're already successful." One reason, he added, is that society is "much more open to outsiders" in top jobs and at elite colleges than it ever was before.

EVEN if successive generations of immigrants manage to become as economically successful as native-born Americans, a big question will remain: How many people do we really want in the United States? From the standpoint of government fiscal policy, Professor Card said, you could argue that the only immigrants you'd want in the United States were those "whose children are going to get Ph.D.'s" and would therefore be economically productive.

Some people might argue that a larger population raises housing prices and causes more pollution, he said. But there can be advantages to size, too. "If you have population growth, you can finance intergenerational transfer systems" like Social Security and Medicare, he said. And lest we forget, he said, "big countries have more power."

Mr. Frey agreed that waves of immigration could help to solidify a country's position in the world. In that respect, he said, Europe and Japan have a problem. "They have a very aging society because they don't like immigrants," he said. "They're going to end up on the back burner of the global economy."

Copyright 2006 The New York Times Company. Reprinted from The New York Times, SundayBusiness/Inside The News, of June 18, 2006.