Earlier this month, students for the first time took a new, and allegedly improved, SAT. The test’s developer included more-contemporary vocabulary and removed penalties for guessing the wrong answer. The changes came with a predictable outcry—complaints, for instance, that too many word problems in the math sections disadvantage some students. There was also a familiar refrain from parents: Why do we have this exam at all? Why do colleges put so much stock in the results? And why-oh-why do our kids have to take so many tests?

It might seem unfair that admissions officers place almost as much weight on a one-morning test as they do on grades from four years of high school, as a 2011 survey from the National Association for College Admissions Counseling showed. But there’s a simple reason for this emphasis on testing: Policy makers and educators have effectively eliminated all the other ways of quantifying student performance.

Classroom grades have become meaningless. Last year a public-school district in northern California decided to score on an “equal interval scale”—meaning every letter grade is assigned a 20-point range. Students who score above 80% get an A. Only those below 20% will be given an F. This is only part of a larger trend.

Figures from the Education Department show that between 1990 and 2009, high-school graduates’ mean GPA rose 0.33 points for women and 0.31 points for men—even while their ACT and SAT scores remained the same. Most of that increase occurred on the lower end of the spectrum, which isn’t surprising. Since high schools are often rewarded for increasing their graduation rates, teachers are fairly reluctant to give out D’s and F’s.

It is possible that beneficiaries of grade inflation are fooling their parents, but they’re probably not fooling their professors. Between 28% and 40% of college freshmen need at least one remedial class, according to research from the National Council of State Legislatures.

College is where grade inflation really takes off. According to a study recently published on Gradeinflation.com, a website run by Stuart Rojstaczer, a former Duke University professor, and Christopher Healy, a Furman University professor, more than 42% of the grades awarded at two-year and four-year colleges are A’s. At four-year schools, the number of A’s has been going up five to six percentage points per decade.

Harvey Mansfield, a professor of government at Harvard, eventually gave in to grade inflation by assigning his students two grades, an official inflated grade for their transcripts and an unofficial grade reflecting what they actually deserved.

Faculty seem to have decided that grades don’t matter. The director of the Yale Journalism Initiative wrote an op-ed a few weeks ago in the Washington Post titled “There’s Nothing Wrong with Grade Inflation.” A recent headline in the Chronicle of Higher Education asks “Why Do Colleges Still Use Grades?”

Several smaller schools no longer do. Alverno College in Milwaukee, the New College of Florida and Fairhaven College in Washington are among those that use portfolios instead of traditional letter grades, allowing students to compile samples of their work for evaluation.

Mark Barnes, author of the “Hack Learning” book series, has argued that subjective grades “turn honest kids into cheaters” and “eliminate the opportunity for self-evaluation.” Alfie Kohn, the author of several books on restructuring education, has concluded that “grades poison everything they touch, undermining intrinsic motivation to learn and warping the whole classroom dynamic.”

Experts interviewed by the Chronicle say that “no one really likes grading.” If it doesn’t work for professors and annoys students, the argument goes, why don’t we just drop these silly letters? But doing so simply kicks the problem of evaluating students upstairs—to graduate schools or employers.

For her book “Inside Graduate Admissions,” Julie R. Posselt watched six highly ranked departments conduct reviews of grad-school applicants. She writes that although administrators said they were taking a holistic approach to admissions, they all placed significant emphasis on applicants’ GRE scores. Some eliminated two-thirds of the candidates based on those numbers.

“Grades are increasingly a lousy signal,” a sociologist explained, “especially at those elite places that just hand out the A’s.” Standardized tests, for all their faults, are the only thing left to judge students by.