At first, the list of colleges deciding during the pandemic to go “test-optional” (meaning that applicants can choose whether or not to submit test scores) included mostly small private institutions — Williams, Amherst, Tufts, Vassar — and the decisions were often presented merely as temporary changes or pilot projects.

But last week brought much bigger news: Janet Napolitano, the president of the University of California, recommended to the system’s Board of Regents that the entire U.C. system go test-optional for the next two years, followed by two years during which the university would become not just test-optional but “test-blind.” In 2023 and 2024, Ms. Napolitano proposed, Berkeley and U.C.L.A. and every other U.C. school wouldn’t consider SAT or ACT scores at all in their admissions decisions.

The university administration, Ms. Napolitano explained, would spend these years trying to come up with its own better and fairer standardized admission test. If it failed, U.C. wouldn’t go back to accepting the SAT and ACT; instead, it would eliminate the consideration of standardized tests in admissions for California students once and for all.

This was a sweeping proposal, especially for such an influential institution as the University of California. And what was so surprising about Ms. Napolitano’s recommendations — which will be put to a vote by the Board of Regents on Thursday — was that they came less than a month after the university’s faculty senate had unanimously accepted the report of a task force supporting the continued use of the tests and proposing to keep them in place for at least the next nine years.

If the Regents concur with Ms. Napolitano this week, it will be a crucial turning point in a national debate about standardized testing that has been going on for decades. Do standardized tests help smart, underprivileged college applicants? Or do they hurt them?

Proponents of standardized tests often make the case that the tests are the least unfair measure in a deeply unfair system. It’s certainly true that the system is unfair from start to finish. Rich kids enjoy advantages over poor kids that begin in prenatal yoga sessions and continue through summer tennis camps, after-school robotics classes and high-priced college-essay coaching sessions. But the data show that standardized tests don’t level that playing field; they skew it even further.

The best predictor of college success overall is a simple one: high school grades. This makes a certain sense. An impressive high school G.P.A. reflects a combination of innate talent and dedicated hard work, and that’s exactly what you need to excel in college. And while standardized test scores have long been found to be highly correlated with students’ financial status, that’s much less true with high school G.P.A. In a recent study, Saul Geiser, a researcher at Berkeley, found that the correlation between family income and SAT scores among University of California applicants is three times as strong as the correlation between their family income and their high school G.P.A.

You can see the same pattern when you look at applicants by race. When Mr. Geiser used high school G.P.A. to identify the top 10 percent of Californians applying for admission to the U.C. system, 23 percent of the pool was black or Latino. When he used SAT scores to identify the top 10 percent, 5 percent was black or Latino.

Here’s another way to look at the numbers: The students who are most likely to benefit from any university’s decision to eliminate the use of standardized tests are those who have high G.P.A.s in high school but comparatively low standardized test scores. These are, by definition, hard-working and diligent students, but they don’t perform as well on standardized tests. Let’s call them the strivers.

A few years ago, researchers with the College Board, the organization that administers the SAT, analyzed students in that cohort and compared them with their mirror opposites: those with relatively high test scores and relatively low high school G.P.A.s. Let’s call them the slackers: self-assured test takers who for one reason or another didn’t put as much effort into high school.

The College Board’s researchers made two important discoveries about these groups. First, there were big demographic differences between them. The slackers with the elevated SAT scores were much more likely to be white, male and well-off. And the strivers with the elevated high school G.P.A.s were much more likely to be female, black or Latina, and working-class or poor.

The researchers’ second discovery was that students in the striver cohort, despite their significant financial disadvantages, actually did a bit better in college. They had slightly higher freshman grades and slightly better retention rates than the more affluent, higher-scoring slackers.

Despite the persistent and compelling evidence that standardized tests penalize low-income students, a lot of us want to believe the opposite: that standardized tests are the tool that can help selective colleges pluck brilliant low-income students out of low-performing high schools. These Cinderella stories do sometimes happen, and when they do, they’re inspiring. But these anecdotal exceptions are overwhelmed by the experience of a large majority of ambitious low-income students, for whom standardized tests have the opposite effect: They construct a wall that separates them from prestigious universities, a wall with a narrow doorway that only well-off kids seem to know how to squeeze through.