In order to ensure that TFs are sufficiently knowledgeable about the often specialized Core courses, many professors spend a great deal of time preparing their TFs and last-minute additions to the teaching staff are often less prepared.

"In the long run, it does not benefit the undergraduate," Todd says.

And Coop officials often come under fire for higher textbook prices they say are a result of unpredictable supply and demand due to the late registration date.

According to Evan P. Mooney, textbook department manager of the Coop, the Harvard Square Coop has a return rate that is 30 percent higher than that of other college bookstores.

Mooney attributes Harvard students' greater tendency to buy books and then return them to the uncertainty of shopping period.

"[Shopping period] is one of the things that makes a Harvard education so expensive," says Owen J. Gingerich, professor of astronomy and the history of science.

Enrollment below the expected level can also drive up the overall cost of a course.

It is Core Office policy not to fire graduate students if eventual enrollment is lower than expected.

To avoid a surplus of instructors, the Core Office gives professors enough funds to hire TFs for only two-thirds of the expected enrollment.

Even with the conservative projections, however, there are occasionally additional TFs in a course, and the cost is passed on to the student.

Professors also say that having a week of lectures before students are committed to the course reduces the week to little more than a sales pitch.

"I have great lectures I give during shopping period because I know that's when it really counts," says Mark A. Kishlansky, professor of history.

Some professors say shopping period effectively reduces the length of the semester by an entire week.

Todd says that last fall, when he taught Literature and Arts C-30: "How and What Russia Learned to Read: The Rise of Russian Literary Culture," he wanted to lay the groundwork for the course in the first three lectures.

"But I knew that for maybe half of the students in the course it would be wasted," he says, adding that he had to compress the material of the first week's lectures into the rest of the semester.