Correction: An earlier version of this article misstated the University of California campus that employs economist Mindy Marks. It is UC-Riverside, not UC-Santa Barbara. This version has been corrected.

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.

The University of the District of Columbia declined to release data on study time. Georgetown and George Washington universities have not given the survey recently.

Evidence of declining study was mostly ignored until 2010, when two University of California economists brought the issue to the fore in a paper titled “Leisure College, USA.”

Philip Babcock and Mindy Marks unearthed previous research, part of a longitudinal study called Project Talent, that showed students of 1961 spent about 24 hours a week studying.

They calculated that those students spent another 16 hours in class time, or 40 hours in total weekly scholarship, giving college, for them, the feel of a full-time endeavor.

By contrast, the typical student today spends 27 hours a week in study and class time, roughly the same time commitment expected of students in a modern full-day kindergarten.

“This is an absolutely enormous change in postsecondary education, possibly as big as anything we’ve seen in the last 50 years,” Babcock said.

The finding has led some critics to question whether college is delivering on its core mission: student learning. Sociologists Richard Arum and Josipa Roksa identified lax study as a key failing of academia in their 2011 report “Academically Adrift,” which found that 36 percent of students made no significant gains in critical-thinking skills in college. Arum’s own research found that students study only 12 hours a week.

“What students are getting is four or five years of country club living,” said Richard Vedder, an Ohio University researcher who studies the economics of higher education.

Some academicians dispute the evidence of a downward trend in study time. They note that the findings are based on different surveys and on the fallible accounts of students. Babcock and Marks say their analysis accounts for those subtleties. The director of the student engagement survey, Alexander McCormick, concurs that the findings are sound.

By many accounts, students are far from lazy — it’s just that things besides schoolwork are consuming more of their time.

“They’re working full time and going to school full time, which I think is absurd,” said Joe Scimecca, a sociology professor at George Mason. “I asked a class recently how many were working, and there were only two who weren’t.”

Dixon, the sophomore from Haymarket, is majoring in tourism, works 23 hours a week at a campus information desk, commutes up to two hours a day and volunteers at church.

“My planner is a wreck,” she said.

Students at several other colleges report the same stressful pace. Karli Wood, a senior at Northern Kentucky University, maintains an A-minus average, even though she works nearly 40 hours a week and commutes up to an hour a day across the Ohio River from her Cincinnati home. She counts her study time in minutes, not hours.

“I don’t mean to sound cocky,” she said, “but if I had more time, I could have had a 4.0.”

Modern technology helps and hinders collegiate study. Students are more efficient in researching and writing term papers now than 50 years ago. They also spend several hours a week using computers for fun, a pastime that did not exist in 1960.

Nationally, few colleges even approach the historical standard of 24 hours of weekly study. Private schools do not report much more study than public ones, and elite schools report only marginally more study time than the less elite. Even among colleges rated “most competitive” in the Barron’s college guide, the survey shows, weekly study averages less than 18 hours.

Colleges that rate high in study time are typically small liberal-arts schools, often set in remote locales. Kenyon College in Gambier, Ohio, DePauw University in Greencastle, Ind., and Centre College in Danville, Ky., all report more than 20 hours of average weekly study for freshmen, seniors or both.

Sweet Briar, on a rural campus outside Lynchburg, is a regional leader in study time. Yet, the school is only modestly selective. Four-fifths of applicants are admitted, and SAT scores average about 1,100 out of a maximum 1,600 points in reading and math.

What sets such schools apart? Pedar Foss, dean of academic life at DePauw, found clues sprinkled across the student survey. DePauw students almost never work off campus, care for relatives or commute long distances. DePauw seniors are twice as likely as students at other schools to read at least 11 assigned books in an academic year. They write more than their peers.

“They’re held accountable for how well they can speak, and how well they can draw upon evidence, and whether they know what they’re talking about,” Foss said.

Another key to study time is one’s choice of major. McCormick, director of the student engagement survey, analyzed 85 majors and found a 13-hour spread in average weekly study. Architecture students studied the most, at 24 hours a week. Further down the list, in descending order: physics (20 hours), music and biology (17), history (15), psychology (14), communications (13) and, at 11 hours, parks, recreation and leisure studies.

“Every one of these colleges has some students who are studying quite a bit,” McCormick said, “and, to balance things out, some students who are studying very, very little.”