New York - Top colleges are filling more of their classes in early-admissions programs that favor affluent families, placing another barrier before poorer students hoping to better themselves through higher education.

Families that need financial aid often wait for the regular round, which starts this month, so they can compare aid offers. Because early-decision programs require a binding commitment to one school in November and boost admissions chances, many slots are taken before lower-income students even apply.

At Northwestern and Duke, about half the spots for this fall's freshman class are already spoken for. Ten years ago, the universities each took about a quarter through early admissions. Vanderbilt expects its class to be as much as 44 percent full by next month, compared with a third a decade ago.

"The scale is definitely tipped to the kids who have more behind them financially," said Bruce Poch, former dean of admissions at Pomona College in Claremont, Calif. The trend of colleges filling up early "has gotten more extreme in recent years."

Such programs aren't helping Jackson Le, a high school senior from Quincy, Mass. His single mother, who emigrated from Vietnam, has a job as a manicurist in a nail salon.

Le has his sights on Boston University. Since he needs to shop around for the best financial aid possible, he didn't apply there for early decision in the fall. The percentage of places filled early at Boston University has doubled to 20 percent over the past seven years. He envies wealthier classmates who are already broadcasting their acceptance letters on Twitter.

"It makes me sad because I wish I had that opportunity to apply early," said Le, 18, an honors student who works as much as 20 hours a week at Starbucks to help pay for college.

The College Board counted 460 schools last year offering early admissions. That's up from about 100 in the 1990s, according to a 2010 study by Christopher Avery, a public policy professor at Harvard University, and Jonathan Levin, an economist at Stanford University. Colleges say scholarships are available to those who apply early, and they are increasing such aid so more low-income students can attend.

Still, their early applicants are far more likely to be from wealthy, white families who hire private college counselors to steer them to such programs, according to a 2011 report by the Center for Enrollment Research, Policy and Practice at the University of Southern California in Los Angeles. Such advisers can cost families thousands of dollars. The early plans "perpetuate social privilege," the researchers said.

A 2011 study of two unnamed northeast liberal arts colleges by professors at Syracuse University and Michigan State reached a similar conclusion. A greater proportion of students from higher-income families, whites and the children of alumni apply through early decision than in the regular pool and are accepted at more favorable rates, even though they have lower grades and test scores than those in the regular round, their data showed.

Acceptance rates for early programs can be more than twice as high as in the regular round, and Duke advertises that advantage on its website. Students applying early have an edge that's equal to about 100 extra points out of 1,600 on the reading and math sections of the SAT entrance exam, according to Avery and Levin.

Colleges say they have increased financial aid for low-income students, with the poorest receiving up to a full ride. Douglas Christiansen, dean of admissions at Vanderbilt University in Nashville, Tenn., said financial-aid packages are identical no matter when students apply and that the school seeks diverse students in both early and regular rounds. Boston University declined to comment.

Universities offer early plans so students can signal their top choice and avoid the hassle of applying to as many as a dozen colleges. The schools say they need to do so for competitive reasons, since the top students are looking to wrap up their choices.

Duke University in Durham, N.C., is taking more applicants early because their qualifications are stronger than in the past, said Christoph Guttentag, dean of admissions. Some 3,180 students applied early - more than twice as many as a decade ago - and 26 percent were accepted last month. Last year, the admit rate in the regular round was 10 percent.

The early pool includes more students who can afford to pay Duke's full cost, which is more than $63,000, Guttentag said. The overall class is more diverse, and 21 percent of current freshmen are African-American and Latino, he said.

"If the opportunity presents itself to be responsive to highly qualified students who have Duke as a clear and unambiguous first choice, we like to take advantage of that," Guttentag said. "Students and families are always going to weigh finances as part of the process."

Northwestern University likes early decision because it lets "some of the best high school students in the country" make a commitment to attend, said spokesman Alan Cubbage. At the same time, the school is reaching out to a diverse group of students, he said. Almost a quarter of its freshman class is African-American or Latino, the most ever. Northwestern, based in Evanston, Ill., is also expanding a program to enroll Chicago Public School graduates to 100 from 75.

Northwestern announced that initiative as part of a group of more than 100 colleges, including Duke, which signed a White House pledge to attract more low-income students.

Even as they make such promises, colleges are catering to students that pay their own way because of the institutions' own self-interest, while limiting opportunities for lower-income families, said Jose Luis Santos, a vice president for higher education at the Education Trust, a nonprofit group based in Washington.

"It's completely unfair," said Santos, the child of migrant workers from Mexico who joined the Marine Corps to help pay for college. "A lot of us are working toward eliminating inequity in college admissions. These policies are exacerbating income inequality."

Students admitted early tend to have a host of advantages. Many are recruited athletes with committed parents who can often afford to pay for training, according to Chris Lincoln, a college consultant who wrote a book about recruiting. Some sports, such as crew and squash, aren't available equally across the U.S., he said.

Williams College in Williamstown, Mass., just admitted 44 percent of the freshman class through its early decision program. About a quarter are recruited athletes for 32 varsity sports, according to Director of Admission Richard Nesbitt.

To level the playing field, Williams now flies in low-income students to the campus before its early admissions deadline and each year has let two or three students out of the commitment if they feel they don't get enough aid after talking with the financial-aid office, Nesbitt said.

Colleges often encourage the children of alumni, who receive preferential treatment, to apply early. The University of Pennsylvania in Philadelphia suggests such "legacies" apply early if they want to get a boost in their chances, according to Eric Furda, dean of admissions. Last month, Penn accepted 54 percent through early decision, tying its record.

Penn is receiving stronger and more socioeconomically diverse early applicants, Furda said. Of the 1,316 admitted last month, 124 were the first in their family to attend college, almost a third more than last year, he said.

Not all early programs are equal. At Penn, students typically apply in November and make a binding commitment to withdraw their other applications if accepted in December, unless they can show they can't afford to attend.

So-called early action programs are similar, except students don't have to go if admitted. A handful of early action programs, including those at Harvard, Yale and Princeton, require that students apply only to their school in that round, though they generally have exceptions for some other nonbinding programs.

Early action plans aren't nearly as discouraging to low-or middle-income families because they can still shop around for financial aid, according to J. Jay Greene, a college counselor with Boca Raton office of Ducerus.

Still, Harvard, until recently, worried about early action's impact on less-fortunate applicants. In 2006, Harvard, in Cambridge, Mass., announced it was scrapping its program because, as then-President Derek Bok said, it tends to "advantage the advantaged" who are savvy enough to know to apply early. Princeton University, in New Jersey, followed suit.

In 2011, the schools reversed themselves, citing the need for such programs to compete for top students. Last month, Harvard admitted 977. Since 82 percent accepted Harvard's admissions offers last year, that means about half the spots could be taken for this fall's freshman class. At Princeton, more than a third could be spoken for.

Harvard said admissions of low-income students have increased since the return of early action. "What matters most is the excellence and promise of the students who matriculate in the fall, not when they apply," said spokeswoman Anna Cowenhoven.

Princeton declined to comment, referring to a statement four years ago that said it had hoped other colleges would also eliminate early admission. Since they didn't, the school said it reinstated the program because it was losing some students who wanted to settle their choice sooner even though their first choice was Princeton.

No doubt, many students love to lock in their choice in the fall. Dave Kreissman, a senior at Trinity, a private school in New York, was admitted to Northwestern through early decision last month. As others sweated out their applications for April admissions, Kreissman, 18, is planning his next moves, such as landing an internship in Chicago with a sports team.

His family had hired a private college counselor, who showed them the statistical edge of applying early, according to his father, Gary, co-founder of an Internet marketing company. Northwestern's early admit rate was 36 percent last month. Last year, only 11 percent got in during the regular round.

"There is definitely pressure to pick a school early, and the numbers dictate it," Dave Kreissman said.