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.

Favorable Rates

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 1600 on the reading and math sections of the SAT entrance exam, according to Avery and Levin.

Seeking Diversity

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, Tennessee, 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, North Carolina, 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.

Early Pool

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, Illinois, 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.

Self-Interest

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.”

Recruited Athletes

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, Massachusetts, 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.