The empty seats started to irk him.
Blair Hedges, a professor of biology at Pennsylvania State University, noticed an increasing number of them in the lecture hall where he taught his biology class. This wasn’t an 8 a.m. distribution requirement snoozer, either; it was a late-morning, advanced-level course designed for majors.
Attendance hadn’t been an issue for Hedges throughout the 1990s, when he estimates that, on average, 80 percent of enrolled students came to his class. But he noticed a decline over the last five years -- so much so that he decided to take an informal tally of his students. What he found was discouraging: Forty to 50 percent of students weren't attending his classes, which mirrored what he heard from colleagues in his department and at other large universities.
“That’s a huge number of students not showing up,” Hedges says.
While longitudinal data to support Hedges' findings on a mass scale are lacking, several researchers have provided a snapshot of attendance patterns. A 2005 survey  of first-year undergraduate students by the Higher Education Research Institute at the University of California at Los Angeles showed that while a majority of college students spend 11 or more hours in class per week, 33 percent reported skipping class and 63 percent said they come to class late “occasionally” or “frequently.”
A similar survey showed that the proportion of students who report coming late to class has jumped from 48 percent in 1966 to 61 percent in 2006 -- evidence, one could argue, of a growing indifference to class in general.
"Maybe it's a cultural thing, relating to multi-tasking and a situation where students are almost too busy to come to class," Hedges says. "It makes sense to show up to lectures. People who hear things and see things and write them down learn better than those who don't have all three of those stimuli coming in. The other students are learning the material but not getting the fine details."
As attendance in Hedges' class has sagged, so too have test scores. Because course material changes each year, he says it's almost impossible to find a standard metric that allows tracking of learning over the years. Still, his attendance survey shows that students who come to his class regularly earn on average one letter grade higher than those who don't.
David Romer, a professor of economics at the University of California at Berkeley, found the same grade-attendance correlation when he surveyed students enrolled in economics courses at three "relatively elite" institutions of various sizes. The results, published in a 1993 article in the Journal of Economic Perspectives, found that among the entire cohort, one in three students regularly didn't attend class during that week. The rate of absenteeism was highest (40 percent) at the large public university, but still notable at the medium-sized private (34 percent) and small liberal arts college (25 percent.)
Institutions the size of UCLA and Berkeley represented a minority of institutions that responded to the 2005 Higher Education Research Institute survey, one indication that absenteeism is widespread. Professors say it's not so much the size of an institution but, among other things, the size of the class that is a likely predictor of attendance. So to the extent that large public universities are most likely to offer lecture hall-filling courses, the issue of class skipping is most pronounced there.
Hedges has a theory about what allows students to skip classes and still pass, and it involves an act that many professors see as pedagogical charity. While some students benefit from reading course lecture material over the Internet, professors are enabling lazy students, he says, by making entire PowerPoint presentations available online to students who use the notes as a substitute for live interaction.
While Hedges typically puts his lecture outlines -- talking points, not details -- online, last fall he removed the material. Students complained, but he says class attendance improved slightly. For future classes, Hedges plans to include some online material because he says it helps students who do attend class.
Will Kalkhoff, an assistant professor of sociology at Kent State University, says he noticed a drop in attendance in his 40-person deviant behavior course when he began posting lecture notes online.
“In general, I think the classes are better when I provide the students with the notes ahead of time, but they are only better for the students who show up,” Kalkoff wrote in an e-mail. He has used PowerPoint for two years and found that students interact in class less than they did when he relied on chalk. "I almost feel like I'm giving a TV show and they are sitting there watching it; you don’t ask questions of the TV."
(According to the 2005 HERI survey, 76 percent of first-year students reported speaking up in class -- although the 40-year study done by UCLA found that students reported less interaction with instructors than those who answered in the earlier sample.)
Not surprisingly, professors say the reputation of a class is an important factor in student attendance. Gary Wyatt, an associate professor of sociology at Emporia State University, found that 110 first-year students at "medium sized" colleges in the Midwest reported an average of three absences from courses that they liked and 5.3 from those in which they didn't. (He published results in a 1992 edition of the journal Teaching Sociology, noting that results are from self-reported memories of classes missed and need to be interpreted with caution.)
Equally intuitive are the results of a yet-to-be peer-reviewed study from three economics instructors at the University of California at Santa Cruz showing that students there most often miss class because a) they are sleeping, b) they are preparing for other classes or c) they feel like the class is "useless."
But that study, looking at all economics classes at UCSC above 50 students over an entire quarter, also found that "there is a surprisingly little correlation between observable characterstics of a class and the attendance," according to Carlos Dobkin, one of the researchers. In other words, whether an instructor used PowerPoint or a chalkboard; whether she spoke English or not, didn't have a noticeable effect on enrollment patterns.
Madeline Donovan, a sophomore at the University of Nebraska at Lincoln, says she can typically tell whether a class is worth attending within the first week. For her, it's often a matter of time management.
"When it's close to a test, I go to every class," she said. "After a test, if something is coming up, I weigh priorities. Sometimes other things are more important than spending an hour-and-a-half learning about things I can see in a textbook."
Other elements factor into whether Donovan goes to class. If it's a large course with no attendance policy, she'll often skip. If it's small and participation factors heavily into grading, she'll go. She says many of her friends use a similar calculus -- although she admits that laziness sometimes enters the equation. Some classmates have an informal competition to see who can skip the most classes in a term and still emerge unscathed. (Facebook groups that brag about skipping class to sleep or to watch The Price Is Right suggest that such contests aren't isolated.)
Donovan keeps one other thing in mind. "I think a lot about tuition money and how much money I'm wasting if I choose to skip class," she says. "There's a pretty big guilt factor, especially if your parents are helping you pay for school."
To some professors, half-filled classrooms are a sign of disrespect.
Mark Muraven, an associate professor of psychology at the State University of New York at Albany, estimates that 50 percent attendance is the norm in his 200-person lecture courses. And it's typically the same students who come to each class.
"What blows me away is that some mornings, I give a quiz and 95 percent of students show up, but then afterward a large group stands up and leaves," Muraven says. "They are already there. They have a pen in hand and decide to go back to bed. I used to take it personally. Now I think it's funny -- I can't explain it."
Skipping class is so much a part of the undergraduate culture, some contend, that the issue doesn't warrant attention or action. Students who want the complete experience will come to class, and those who skip are making a choice.
That's Patricia Hawley's mindset. She's an assistant professor of psychology at Kansas State University who sees roughly 65 to 90 percent attendance in her classes. Hawley posts online notes because she says she has no evidence that doing so means students are less likely to come. Plus, no student should feel lost, she says.
"Other professors get annoyed when students don't show up," Hawley says. "When I was in college, I had a life. I had emergencies and jobs. This isn't a fun time for all students. They aren't cutting class because they're drinking or going to frat parties. They are adults. Sometimes life intervenes."
Brian Starks, an assistant professor of sociology at Florida State University who teaches a 65-person introduction to sociology course, says some students come to college with the mindset that lectures are largely a waste of time.
“When I first got here, I tried to get the unmotivated ones to go to class, and I felt I was fighting a losing battle," he says. "Even when I said, 'you’re going to fail,' they didn’t seem to care, so I stopped engaging them.”
But Janet Stemwedel, an assistant professor of philosophy at San Jose State University who often ruminates about attendance issues , says she isn't ready to "do triage" -- though that continually sets her up for disappointment. In a 20-person class this spring, only six attended one session and two didn't open their mouths, leading to what she called a "painful" hour.
"If people think skipping class is a victimless crime, they are wrong. It undercuts dynamics of discussions and debates," she says.
While it isn't an irrational choice for students to skip some classes -- she can remember several as a student that added little value -- Stemwedel says there are many more cases when professors lose students because they fail to frame their introduction to the class in the right way. She tells students in a philosophy of science course, taken largely by science majors who are fulfilling a requirement, that what they will hear in lecture will change the way they think about their field. (Not to mention the fact that participation is a part of the final grade.)
And some faculty members report that absenteeism just isn't a problem. Susan Krauss Whitbourne, a professor of psychology at University of Massachusetts at Amherst, says that her introductory psychology course -- the typical survey course that would lend itself to skipping -- is at least 80 percent full each session.
Professors need to be innovative if they expect high attendance, she says. "People who complain about the student often aren't those putting in that much effort themselves. Either they are inept or they don't care."
Or, as some faculty see it, their colleagues are giving students too much leeway.
Jeannette Jones Haviland, a professor of psychology at Rutgers University at New Brunswick, says she gets nearly 100 percent attendance in her adolescent psychology course of more than 100 students. She goes the pop quiz route, handing out the exams at the start of many classes to see if students have completed the reading. Anyone with a cumulative quiz grade above a certain level doesn't need to take the midterm.
For years, Dan Clawson, a professor of sociology at the University of Massachusetts at Amherst, asked students in his sociology courses -- some of which top 200 people -- to complete a one-page response paper due on the first day of each week's class. Students could write three five-page papers and avoid taking any final exam, and most in the class chose that option. Clawson said the disadvantage of the policy was that some students saw no incentive to come to class, particularly because his courses are taken by a non-trivial number of students in other fields who have limited interest in the topic.
Attendance would drop below 50 percent late in the semester, once students felt they had some mastery of the topics covered in the papers. To address the problem he reluctantly changed the policy last fall, replacing the response papers with six unannounced in-class quizzes that account for 25 percent of the final grade.
According to Clawson, attendance never again fell below 80 percent and usually hit 85 percent. But a new problem emerged: Students thought that because they came to class they could slack off on the reading. For the in-class quizzes, students did much better at answering questions based on lectures than at answering questions based on readings, he says. Students clearly read less of the material, and they read it less carefully.
Others have found troubling their role as an attendance enforcer. Kalkhoff, the Kent State professor, says he used to have what he calls a “hardcore” attendance policy. Students rarely skipped, but he grew “weary of being a police officer,” so he dropped the policy. “I spent a lot of time tracking down validity of excuses and listening to people, spending way to much time on that," he says.
Hedges, the Penn State professor, says it's nearly impossible to manage such a policy once a class gets into the hundreds, which brings the debate back to where it began.
In his first 10 years teaching at Florida State, Clawson never taught a class in which enrollment exceeded 75 students. Now, 27 years into his career there, he routinely teaches classes of more than 200 students.
“That changes the dynamic significantly," he says. "I've always relied on establishing a rapport with students. Missing class has always been an issue, but because of size, it's certainly gotten worse and harder to monitor."