NEW YORK — An unprecedented study that followed several thousand undergraduates through four years of college found that large numbers didn’t learn the critical thinking, complex reasoning and written communication skills that are widely assumed to be at the core of a college education.

Many of the students graduated without knowing how to sift fact from opinion, make a clear written argument or objectively review conflicting reports of a situation or event, according to New York University sociologist Richard Arum, lead author of the study.

The students, for example, couldn’t determine the cause of an increase in neighborhood crime or how best to respond without being swayed by emotional testimony and political spin.

Arum, whose book “Academically Adrift: Limited Learning on College Campuses” (University of Chicago Press) comes out this month, followed 2,322 traditional-age students from the fall of 2005 to the spring of 2009 and examined testing data and student surveys at a broad range of 24 U.S. colleges and universities, from the highly selective to the less selective.

Forty-five percent of students made no significant improvement in their critical thinking, reasoning or writing skills during the first two years of college, according to the study.

After four years, 36 percent showed no significant gains in these so-called “higher order” thinking skills.

Combining the hours spent studying and in class, students devoted less than a fifth of their time each week to academic pursuits.

By contrast, students spent 51 percent of their time – or 85 hours a week – socializing or in extracurricular activities.

The study also showed that students who studied alone made more significant gains in learning than those who studied in groups.

“I’m not surprised at the results,” said Stephen G. Emerson, the president of Haverford College in Pennsylvania.

“Our very best students don’t study in groups. They might work in groups in lab projects. But when they study, they study by themselves.”

Arum concluded that while students at highly selective schools made more gains than those at less selective schools, there are even greater disparities within institutions.

“In all these 24 colleges and universities, you have pockets of kids that are working hard and learning at very high rates,” Arum said. “There is this variation across colleges, but even greater variation within colleges in how much kids are applying themselves and learning.”

For that reason, Arum added, he hopes his data will encourage colleges and universities to look within for ways to improve teaching and learning.

Arum co-authored the book with Josipa Roksa, an assistant professor of sociology at the University of Virginia.

The study, conducted with Esther Cho, a researcher with the Social Science Research Council, showed that students learned more when asked to do more.

Students who majored in the traditional liberal arts – including the social sciences, humanities, natural sciences and mathematics – showed significantly greater gains over time than other students in critical thinking, complex reasoning and writing skills.

Students majoring in business, education, social work and communications showed the least gains in learning.

However, the authors note that their findings don’t preclude the possibility that such students “are developing subject-specific or occupationally relevant skills.”

Greater gains in liberal arts subjects are at least partly the result of faculty requiring higher levels of reading and writing, as well as students spending more time studying, the study’s authors found.

• Sara Rimer