(CBS) -- New research shows that nearly half of high school seniors, 47 percent, graduated last year with an "A" average, but average SAT scores fell 24 points in the same period, CBS News reports.
The authors of the study said the trend shows that grades have been inflated over the past two decades.
"Historically, what we find, is that the best predictors of college success is a combination of high school GPA and SAT scores, but one of the things we've been noticing is that high school GPAs are drifting up, and up, and up," Michael Hurwitz, co-author of the study said.
Grade inflation means students are more often earning the same exact GPA as each other, making college admissions more complicated.
"The variation in GPAs have actually decreased by 10 percent," said Hurwitz.
"We don't know exactly why, but we have some theories," he said. "One of the metrics for ranking magazines, like, U.S. News & World Report, is the fraction of students in the top 10 percent or the top 25 percent of their classes, so there's an incentive for colleges to get those numbers high because there's a potential for the rankings to increase."