Add this to the list of consequences of rising college tuition: Students getting better grades than they deserve.

A’s were the most common grade on college campuses in 2013, accounting for 45% of grades awarded to students, according to an analysis of grade data at more than 80 schools by Stuart Rojstaczer, an independent researcher, and Chris Healy, a computer science professor at Furman University. By contrast, college students were most likely to get C’s leading up to the Vietnam War, accounting for about 35% of grades awarded. The two researchers have been collecting and reporting on grade data for years. Monday’s release marks the latest version of their analysis.

The researchers’ data shows how A’s have become the most common grade awarded at colleges. Stuart Rojstaczer and Chris Healy

So how did we get here? There were two distinct periods of grade inflation, according to Rojstaczer. The first began during the Vietnam era, when many professors began elevating grades in part to keep male students from flunking out and being forced into the draft. But flagship public colleges and private schools inflated grades beyond what was required to keep students from going to war.

Their rationale, Rojstaczer said, was to start awarding grades that were based more on a national average, so instead of comparing students with each other, they compared them to students at other schools. That meant that for example, fewer students got C’s because while they might have been doing average work on their campuses, their work wasn’t average compared with students at regional schools, the teachers reasoned.

The second, modern era of grade inflation, which began in the 1980s, has more to do with money than shifting academic standards. As college tuition rose, eating an ever larger chunk of families’ income, university leaders and parents and students began to see college as more of a commodity, said Rojstaczer. That mindset fueled a desire among administrators to keep families happy.

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“If you’re going to treat a student as a customer, the customer is always right,” said Rojstaczer, who is a former Duke University professor and novelist. “You want to please them and how do you please them? You give them the grades they want instead of the grades they deserve.”

Some have argued that the higher grades reflect a higher caliber of student. While Rojstaczer and Healy acknowledge that may be true at some universities, they say there hasn’t been a significant enough change in the quality of students since the 1980s to account for the uptick in grades during that period.

Though students may like getting more A’s, grade inflation can dilute the quality of their education, Rojstaczer said. “It reduces the energy level in the classroom when a student walks in knowing that simply by showing up they can get a B+ or better,” he said. “Not all of them, but a significant percentage of them are simply going to show up.”

Some colleges have taken stabs at clamping down on grade inflation. Princeton University enacted and then ultimately abandoned a policy that banned any department from awarding more than 35% A grades. Wellesley College, the all women’s school in Massachusetts, is known for its policy that requires the mean grade in introductory level courses with 10 students or more not exceed a B+.

While these kinds of policies are successful at the university level, Rojstaczer said he’d like to see a more coordinated national effort by university leaders to make sure students get the grades they deserve. “This is in a sense nothing new, the intensity and quality of the educational experience at universities has waxed and waned for hundreds of years and we’re in an era where it’s on the downside,” he said.