Over the past half-century, the amount of time college students actually study — read, write and otherwise prepare for class — has dwindled from 24 hours a week to about 15, survey data show.

And that invites a question: Has college become too easy?

Ashley Dixon, a sophomore at George Mason University, anticipated more work in college than in high school. Instead, she has less. In a typical week, Dixon spends 18 hours in classes and another 12 in study. All told, college course work occupies 30 hours of her week. Dixon is a full-time student, but college, for her, is a part-time job.

“I was expecting it to be a lot harder,” said Dixon, 20, of Haymarket. “I thought I was going to be miserable, trying to get good grades. And I do get good grades, and I’m not working very hard.”

Declining study time is a discomfiting truth about the vaunted U.S. higher-education system. The trend is generating debate over how much students really learn, even as colleges raise tuition every year.

Some critics say colleges and their students have grown lazy. Today’s collegiate culture, they say, rewards students with high grades for minimal effort and distracts them with athletics, clubs and climbing walls on campuses that increasingly resemble resorts.

Academic leaders counter that students are as busy as ever but that their attention is consumed in part by jobs they take to help make ends meet.

Consider George Mason, Virginia’s largest public university and a microcosm of modern academia. Some students care for dependents. Many commute to class. Seventy percent of seniors hold off-campus jobs. George Mason students spend 14 hours, on average, in weekly study, close to the national average.

“It’s not enough,” said Peter Stearns, the George Mason provost. “And it’s a figure that troubles us, not only at Mason but in higher education generally.”

The university has responded by launching an honors college and an undergraduate research initiative in recent years — driven, Stearns said, by “the need to create a more challenging undergraduate environment.”

Tradition suggests that college students should invest two hours in study for every hour of classes. The reality — that students miss that goal by half — emerged from the National Survey of Student Engagement, a research tool for colleges that examines the modern student in unprecedented detail.

The survey, first published in 2000, queries freshmen and seniors. It reveals that study time can vary widely by college and by major. Architecture majors, for example, study 24 hours a week, while marketing majors put in only 12.

Colleges are not required to publish survey results. The Washington Post asked prominent colleges in Maryland, Virginia and the District to disclose their survey data on study time. Only at Washington and Lee University, in Virginia, did students report as many as 20 hours of weekly study.

At Sweet Briar College, a private women’s school in Virginia, students reported 19 hours of study in an average week. Weekly study among seniors averaged 18 hours at St. Mary’s College of Maryland, 17 hours at the College of William and Mary, 16 at the universities of Maryland and Virginia and Catholic University, 15 at American University and 13 at Howard University.