Overall, the correlation was a loose one. Test scores predicted only 20 percent of the variation in students’ GPAs.  In other words, students with the same test high scores had wildly different GPAs at school the following year. At first glance, the test doesn’t seem very good at discerning A students from B students. Seventh-grade GPAs were twice as likely to predict ninth-grade achievement than test scores.

“People say the SHSAT is objective and that grades are unreliable,” Taylor said. “Schools and teachers have different subjective grading standards and grades are all over the place. The exams were designed to be a uniform metric. It’s ironic that the exams don’t predict as well as grades.”

One might wonder if girls could be taking easier classes or not as many math and science classes once they get to high school and perhaps that is why girls are getting higher grades. But Taylor checked and he found that girls were, in fact, well-represented in math and science classes in ninth grade and doing very well in them.

https://hechingerreport.org/the-problem-with-high-stakes-testing-and-women-in-stem/