But life was not easy at N.Y.U., where, as fate would have it, she also missed the cut for standard admission. Instead, she was admitted to the university’s Liberal Studies Program, a two-year track for slightly weaker applicants, who are guaranteed enrollment in a bachelor’s program their third year.

Ms. Nam held off notifying N.Y.U. about her intention to leave until the end of her year there — and held herself aloof from campus life.

“I knew that I was going to be leaving in a year, so I didn’t want to make any BFF’s,” she said. “It put me in an awkward position. I had no connections with N.Y.U. — it was just a steppingstone for Cornell. A lot of people at N.Y.U. got jealous and cut me out of their lives. It was messy.”

The dean of the Liberal Studies Program at N.Y.U., Fred Schwarzbach, was critical of students who enter knowing their stay will be temporary. Without commenting specifically on Ms. Nam, he said, “In general, we would not admit a student unless that student were committed to a four-year undergraduate experience.”

Still, the benefits of deferred admission can be attractive for both students and colleges.

For years, SUNY Geneseo was on the receiving end of the phenomenon, losing sophomores to Cornell year after year. “A lot of students who apply here also apply to Cornell,” Mr. Caren said. “When Cornell says it will defer their admission, they enroll here for a year. Then they come to the dean’s office and say, ‘Well, I’m leaving.’ We picked up on this, and we decided to do it ourselves.”

Two years ago, Geneseo, the most selective liberal arts college in the state system, began offering students a guaranteed-transfer admission for the following fall. Those students must receive a 3.0 grade-point average from any accredited institution. Geneseo sent out 200 such offers, but only about 15 students accepted.

A more popular program delays admission until the spring semester for hundreds of applicants who are academically stronger than the first group. Mr. Caren said Geneseo last year offered 500 students the option of arriving in the spring, or the following fall; 178 ended up enrolling, up from 50 seven years ago. Though not required to study elsewhere, virtually all do, and more than a third enroll in a four-year college for a single semester.