"Women who thought they would major in economics often become discouraged when they don’t get sufficiently high grades in introductory courses. Men are far less likely to be discouraged by similar grades. In other words, the gradient of major choice with respect to grades in the “gateway” courses is steeper for women than for men."Amanda Hess at Slate summarizes the article, "Women May Be Underrepresented in STEM Because They're Too Concerned With Grades." Similarly, Catherine Rampell writes that "Women should embrace the B’s in college to make more later." These articles, I think, miss a bit of nuance.
I don't think the real issue is that young women are just more "grade-grubby" than young men-- which is actually a pretty harmful stereotype. Grades serve as a signal, both to others and to the student. As Goldin notes, male students disproportionately choose to study economics before entering college. Economics professors are also disproportionately males. Economics grad students, who will be the undergrads' teaching assistants, are disproportionately males. A female undergrad may wonder if she really "belongs" among economists. So if she gets a B in Econ 101, she may put more weight on that than a male student would. If she already had doubts about whether she belonged in the major, she's going to put more weight on the signal from her grade.
I don't think Goldin meant to imply that college women are just "in it for the grades" more than college men. Their decisions on major are more sensitive to grades, but for reasons other than perfectionism. This is why Goldin emphasizes Janet Yellen's nomination to head the Federal Reserve as an important milestone that could draw more women into the field, by showing them that they belong. She writes, "Yellen’s ascension at the Fed will show more women that economics isn’t an exclusively male field."