He says students sometimes add his course as much as two weeks into the semester because, "once they [get] a real feel for a particular course they want to drop it."

Latham says although it is "disruptive" to have students coming in and out of his class during shopping period, he does not take it personally.

"I'm not going to be offended, because I know they need to shop another course," he says.

He and other professors say that despite the inconveniences, they believe shopping period is unique and useful to students.

"I think its kind of fun," Latham says. "It's a Harvard tradition."

Jerome Kagan, Starch Professor of Psychology, echoes his sentiments.

"I don't mind it," he says. "Students are trying to make the most of their education."

Kagan, whose Core course, "Social Analysis 56: Children and Their Social Worlds," has drawn hundreds of students in the past, says he doesn't do anything differently in a lecture during shopping period.

"Certainly we want students to take the course," he says. "But I don't change my presentation."