Students flooded residential college deans’ offices across campus Monday as the deadline to change Credit/D/Fail course enrollments to letter grades approached at 5 p.m.

If last year is any indication, students changed about half of Credit/D/Fail course registrations to letter grades before the deadline yesterday. More than half of Credit/D/Fail course registrations were changed to grades during the 2009-’10 academic year, said Rebecca Friedkin GRD ’94, a senior researcher at the Office of Institutional Research. Though Yale College Dean Mary Miller said the Credit/D/Fail option is intended to allow intellectual experimentation, data from the Registrar’s Office and interviews with students suggest that the program is most popular in students’ final year of study.

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“I’d hate to think that the purpose of Credit/D/Fail, which is to encourage students to try new things, is being undermined in any way,” Miller said. “The purpose is not to help busy people to structure their busy lives.”

Associate Registrar Daria Vander Veer ’87 told the News that 37 students in the class of 2011 took at least one course Credit/D/Fail their first semester at Yale. From that graduating class, more students used the grading option each semester, with 531 students choosing the option this fall.

Two seniors interviewed said Credit/D/Fail is an attractive option because they must devote more time to senior essays. Another senior in Branford College, who asked to remain anonymous so he could speak candidly, said he is taking the psychology lecture “The Modern Unconcious” Credit/D/Fail to make his last semester easier.

“I don’t go to class, and I really don’t study that hard for the tests,” he said.

Meg Urry, chairman of the Physics Department, said she was surprised that upperclassmen take courses Credit/D/Fail more often than freshmen, adding that she thinks the option is best suited to freshmen who wish to explore different areas of study. She said students should not concern themselves with grades and instead focus on learning.

“It’s going the wrong direction,” she said. “The longer people are at Yale, the more the they should recognize it’s about what they learn, not what grade they get.”

Another three students interviewed said they expected Yale courses to become increasingly difficult as they progressed through their undergraduate careers — so as freshmen, they tried to avoid using one of the four Credit/D/Fail opportunities Yale College affords students. Two students said freshmen may use Credit/D/Fail less to allow themselves to major in any of the disciplines they study in introductory courses.

Dylan Levings ’14 said that freshmen also are less familiar with the system than their older counterparts. But Hilary Rogers ’13 said she registered at least one course Credit/D/Fail during each of her four semesters at Yale, though she switched them all to letter grades before the deadline.

“It’s nice to have that plan B if something goes wrong,” Rogers said.

Sam Ooletz ’14 said he began both “Introduction to Macroeconomics” and “Introduction to Environmental Engineering” on the Credit/D/Fail scale this semester in case his five-course workload grew too heavy. He said he changed his engineering course to a letter grade, as he is now doing well, and that he also decided to change his economics grade, though only after taking a midterm for the course Monday.

Philosophy professor Shelly Kagan, whose “Introduction to Ethics” course saw 43 percent of enrolled students opt for the Credit/D/Fail scale last spring, said he knows many of his students begin his courses Credit/D/Fail because of his reputation as a hard grader, and that they often decide whether to change to letter grades after they receive grades for their first papers.

Miller said she is encouraged that over 50 percent of courses registered as Credit/D/Fail were converted to letter grades last year.

“It shows that students start the classes and get engaged and find out, ‘I can do this,’” she said, “which could open different fields of study.”

Seven percent of enrollments were ultimately registered as Credit/D/Fail during the 2009-’10 academic year.