A C grade really once was average, or at least typical: In the 1960s, it was the most commonly awarded grade in college courses.

Not anymore. By 2007, 83 percent of all grades at a sample of 200 four-year colleges and universities were A's and B's. And research from a former Duke University professor found that A's have been the most commonly awarded grade at four-year colleges since the 1990s:

But new research suggests it's possible to reverse the grade inflation trend.

How Wellesley tackled grade inflation

Wellesley College used to be one of the worst offenders. In 2000, the average course grade awarded was a 3.55, an A-minus. Then, in 2003, Wellesley decided enough was enough. The college created a new rule: average final grades in classes at the introductory or intermediate level (a 100-level or 200-level class, in college catalogue terminology) should be no higher than a B-plus.

Professors could exceed those limits, but they'd have to explain themselves in writing to the administration if they did. The change applied to about two-thirds of Wellesley's academic departments, which were awarding grades that exceeded the cap.

Research on the effects of the change, published in the Journal of Economic Perspectives in 2014, suggested it successfully reversed the upward trend in GPAs. Here's what the college learned.

1) When you require professors to give lower grades, they give lower grades

The researchers — Kristin F. Butcher and Patrick J. McEwan, both Wellesley economics professors, and Akila Weerapana, an associate professor at Wellesley — found the effect on the grades students received in their classes was immediate and unsurprising:

Students were about 18 percentage points less likely to get an A or A-minus after the change than they were before. B's became much more common. And the proportion of students who graduated magna cum laude — the second-highest honor for graduating seniors — dropped from 20 percent to 16 percent.

But students in departments that historically had given high grades continued to get high grades, relatively speaking. Academic departments that weren't subject to the cap, which included biological sciences, chemistry, physics, and economics all still gave slightly lower grades than departments where the restriction took effect.

2) Students were more likely to major in economics and the sciences

So were higher grades in humanities classes luring students away from science? The Wellesley data, while a small sample, indicates that grades affected students' choice of major. But students were more likely to switch within disciplines (from sociology to economics, for example) than they were to leave the humanities.

Economics, the most popular major at Wellesley and one that had not been affected by grade inflation in the past, gained new students; other social science disciplines saw enrollments decline.

3) Students weren't as happy with their professors

Research has suggested evaluations of professors can turn into a feedback loop: good grades make students more likely to rate professors highly. Because those ratings can come into play when professors are being considered for tenure or promotion, faculty become more lenient graders to curry favor with students. At Wellesley, students in departments affected by the grade cap tended to give professors lower ratings after the change took effect.

4) Black students were disproportionately affected

After the grade cap was imposed, the proportion of B's increased as the proportion of A's fell. This suggests that students who were receiving the "lowest A-minus" — barely meeting the bar for the grade — were more likely to receive a B-plus after the change. Black students saw a larger-than-average drop in grades, as did students with lower SAT scores.

The researchers put the best possible interpretation on this, suggesting that a more equal grading policy among different departments at the college will do a better job of demonstrating which students need help. But grading is an imperfect, subjective science. The burden of grade deflation appears to have fallen harder on black students than on others.

5) Some students report that lower grades could hurt their job prospects

In the grade inflation arms race, Wellesley disarmed unilaterally. As grades at the private liberal arts college fell after the policy change, they continued to rise everywhere else. That has led to worries from students and recent alumni that the college is putting its graduates behind in the job market.

"They point to examples of web-based job application systems that will not let them proceed if their GPA is below a 3.5," the authors wrote. "The economist's answer that firms relying on poor information to hire are likely to fare poorly and to be poor employers in the long run proves remarkably uncomforting to undergraduates."

The answer, the authors suggest, is for other colleges to join Wellesley to stop grade inflation.