The phone call sent Carla Cain-Walther into shock: The Media teen, from a large, single-parent family of adopted children, was getting a free ride worth nearly $50,000 a year to a small liberal-arts college in Massachusetts.

For Cain-Walther, known simply as Baby Girl until adopted at 9 months old, it was a pleasant turn of fate.

"It was like one of the most amazing feelings. I just started sobbing," recalled Cain-Walther, 20, now a sophomore English major and poet at Williams College. "I thought maybe there is such a thing as fate, or maybe things do fall in place the way they're supposed to."

She is among 3,000 high-achieving, low-income students nationally who have attended high-end private colleges through the nonprofit QuestBridge program. The group includes more than 650 who were directly matched with 25 partner colleges and got all expenses paid, and others who got substantial aid or a free ride because of their low income.

Started by a California emergency-medicine doctor in 2004, the program has run for several years at Princeton University and Swarthmore College and is expanding this year to the University of Pennsylvania and Haverford College.

Palo Alto-based QuestBridge aims to identify students previously underrepresented on the campuses of America's most selective colleges: Those of modest financial means.

Its higher mission: "To reinvigorate America with more thoughtful and sincere leaders, drawn from the lowest economic quartile," said Michael McCullough, founder and president.

A 2004 report by the Century Foundation in New York found that only 3 percent of students at the nation's 146 most selective colleges came from families whose incomes were in the bottom 25 percent.

QuestBridge isn't the only program that recruits low-income students for colleges, and some schools do extensive recruiting of their own.

But it has been gaining respect for helping schools diversify faster. The average income of a QuestBridge family is $32,000, with few coming from families with incomes greater than $60,000.

"We were seeing those students in our pool, but not as many as Quest was able to identify," said Jim Bock, admissions dean at Swarthmore, which has taken 30 QuestBridge scholars and will add 15 in the fall among its 395 freshmen.

Penn is pleased with its 64 incoming QuestBridge scholars, who include a number of first-generation college students, many of them from public schools. Among them are two from Central High, an academic magnet in Philadelphia.

Haverford accepted 17 QuestBridge students. Princeton took 32.

QuestBridge schools cover tuition, room, and board. Many also pay for books, supplies, and travel, and offer work-study jobs to help with other expenses.

Participating colleges contribute 70 percent of QuestBridge's budget. The rest is from donations.

Candidates come from poor rural areas, urban centers, and even affluent suburban and private schools. One of Penn's scholars is from Friends Select in Center City.

"We're able to reach into areas of the country which are hard for individual colleges to get into," McCullough said.

QuestBridge e-mails honors and Advanced Placement teachers nationally, and networks with local groups to recruit students.

In a way similar to medical school selection, students make their top choices, and so do the colleges. Then students are matched with the top choice that wants them.

Dante L. Benson, a junior Asian-studies major at Pomona College in California, couldn't believe the program plucked him from Camden.