At the time, most states required students to complete just one (and in some cases zero) math course to graduate. None required three. But in reaction to the report, states across the country began revamping their curriculum. By the time the class of 1994 was graduating, 40 states had raised minimum math requirements.

It wasn’t the first time the federal government had pushed states to rethink coursework. Back in the ‘50s, during the heat of the Cold War, the government devoted federal funding to helping states rethink science classes so the country would be better prepared to compete with the Soviets. And in recent years, the Obama administration pushed schools and even the entertainment industry to invest in STEM education, suggesting that students would need more and better science, technology, engineering, and math courses to compete in a global economy and that people with degrees in STEM fields earn more than many of their peers.

Yet Goodman, who used to teach high-school math in Watertown, Massachusetts, said during a phone interview that despite all the talk, there was little causal evidence to link how much math coursework students do with their earnings later on. So he started looking at Census data and high-school transcripts from the 1980s and ‘90s. Ultimately, he found big differences in outcomes for black students—but not for white students—after states raised minimum requirements. Earnings for black students that attended high school in states that had passed reforms went up by more than 3 percent. (Goodman focused on black and white students in part because his calculations relied on assigning students’ state of birth as a proxy for where they attended high school, and Asian and Hispanic students were much more likely to be foreign-born. Data limitations didn’t allow him to identify students who were born outside the U.S., but graduated from American schools.) That was especially true for black students who graduated from public schools with lots of students of color. He found that when states increased math requirements, each additional year of math had a return of about 10 percent, or about half the return to a year of high school.

The findings suggest several things, including that math coursework makes up a good portion of the gains a student makes through a year of schooling. Goodman isn’t suggesting that history and English don’t matter, but he is suggesting that math seems to matter a lot. And, crucially, that closing racial disparities in high-school math could help limit disparities in earnings later on.

It’s worth digging into that last point, and Goodman is up front about the fact that he doesn’t have all the answers, but when states raised math requirements, the increased coursework happened at relatively low levels. In other words, with the updated requirements, students were more likely to complete algebra or geometry, not higher-level courses like calculus. And one of the reasons white students weren’t really affected by curriculum changes is that they were already taking the classes anyway. Black students weren’t.