You can lead a student to knowledge, according to an old academic saying, but you can't make him or her think.

I recently wrote about the possibility of testing and certification for what I called a "college-level GED." I heard from a number of readers who supported the idea, but the most thoughtful question I received went like this: What about the "critical thinking" skills that we traditionally expect campus academic life to teach and encourage?

I agree. Critical thinking is the brain's investigative reporter. It questions assumptions and requires more than the memory to pass most standardized tests.

But we do have tests for that. For example, the Collegiate Learning Assessment gives a 90-minute essay test to freshmen and seniors that aims to measure gains in critical thinking and communication skills.

However, recent studies of CLA results reveal another major problem in how little critical thinking is being taught. One new book, "Academically Adrift: Limited Learning on College Campuses," by sociologists Richard Arum and Josipa Roksa, questions whether many of today's college students are learning much on campus that they didn't already know.

Following CLA results and other data for 2,300 students at 24 public and private colleges, Arum, of New York University, and Roksa, of the University of Virginia, startled the academic world with their finding that 36 percent of students made no significant gains in critical thinking and communication skills from their freshman to senior years.

That tends to confirm what reader Jerre Levy, a retired University of Chicago professor, wrote: "I wish with all my heart that a college degree implied that the person holding that degree was capable of critical thinking. However, this is, sadly, not true."

Among the jaw-dropping examples Levy related was a senior who reacted with resentment to a two-week take-home assignment to critically evaluate a scientific journal article.

The professor specifically requested a hard-eyed assessment of strengths and weaknesses in the article's sources, methods and conclusions. She did not, repeat, not want students simply to summarize the contents.

Yet when the students returned their papers, she recalled, one offered nothing but what Levy said she didn't want: "a content summary, without a single evaluative statement." When the student complained about her zero grade, Levy explained the goose egg. The student argued back indignantly, "But that would have required thinking!"

"If students can get a degree from the University of Chicago without having either the will or capacity to think," Levy said, "then it is certainly true of less selective universities and colleges."

Ohio University's Richard Vedder, my former economics professor who gave me the collegiate GED test idea, is even more blunt: "Universities are becoming more like country clubs," he said, with climbing walls, indoor tracks and other luxuries that give students "something else to do with their free time besides drink and have sex."

Vedder, who divides his time between teaching, researching as an adjunct scholar at the conservative American Enterprise Institute and directing the Center for College Affordability and Productivity, blames grade inflation and other perverse incentives, like too much free time.

That would be just another reason for us Americans to develop more innovative alternatives to college, like alternative GED-style certifications of what individuals actually know, not just how many classes they have taken.