A new study provides disturbing answers to questions about how much students actually learn in college — for many, not much — and has inflamed a debate about the value of an American higher education.

The research of more than 2,300 undergraduates found 45 percent of students show no significant improvement in the key measures of critical thinking, complex reasoning and writing by the end of their sophomore years.

One problem is that students just aren’t asked to do much, according to findings in a new book, “Academically Adrift: Limited Learning on College Campuses.” Half of students did not take a single course requiring 20 pages of writing during their prior semester, and one-third did not take a single course requiring even 40 pages of reading per week.

That kind of light load sounded familiar to University of Missouri freshman Julia Rheinecker, who said her first semester of college largely duplicated the work she completed back home in southern Illinois.

“I’m not going to lie,” she said. “Most of what I learned this year I already had in high school. It was almost easier my first semester (in college).”

Three of the five classes she took at Missouri were in massive lecture halls with several hundred students. And Rheinecker said she was required to complete at least 20 pages of writing in only one of those classes.

“I love the environment, don’t get me wrong,” she said. “I just haven’t found myself pushing as much as I expected.”

The study, an unusually large-scale effort to track student learning over time, comes as the federal government, reformers and others argue that the U.S. must produce more college graduates to remain competitive globally. But if students aren’t learning much that calls into question whether boosting graduation rates will provide that edge.

The research found an average-scoring student in fall 2005 scored seven percentage points higher in spring of 2007 on the assessment. In other words, those who entered college in the 50th percentile would rise to the equivalent of the 57th after their sophomore years.

Among the findings outlined in the book and report, which tracked students through four years of college:

l Overall, the picture doesn’t brighten much over four years. After four years, 36 percent of students did not demonstrate significant improvement, compared to 45 percent after two.

l Students who studied alone, read and wrote more, attended more selective schools and majored in traditional arts and sciences majors posted greater learning gains.

l Social engagement generally does not help student performance. Students who spent more time studying with peers showed diminishing growth and students who spent more time in the Greek system had decreased rates of learning, while activities such as working off campus, participating in campus clubs and volunteering did not impact learning.

l Students from families with different levels of parental education enter college with different learning levels but learn at about the same rates while attending college. The racial gap between black and white students going in, however, widens: Black students improve their assessment scores at lower levels than whites.