The AP reports on the same study; besides the researchers’ findings on the gender gap, they also discovered something distressing:

In most states they reviewed, and at most grade levels, there weren’t any questions that involved complex problem-solving, an ability needed to succeed in high levels of science and math. If tests don’t assess these reasoning skills, they may not be taught, putting American students at a disadvantage to students in other countries with more challenging tests, the researchers said.