Honestly, I'm tired of the bs excuse that girls are compliant, mature, and hardworking used to justify gender bias. A lot of girls are immature, less hardworking and misbehaving just like boys. Studies tend to show, females have an advantage in terms of grading because, they tend to have their grades up higher even for the same academic abilities. Even this one shows it: https://www.the-independent.com/news/education/education-news/female-teachers-accused-of-giving-boys-lower-marks-6943937.html#comments-area

However, the excuse that "girls are more compliant, mature and hardworking than boys in school" is somehow ALWAYS the reason. Thing is, teachers do that even when girls misbehave. Study finds, lenient with girls when misbehaving. They discourage bad behavior in boys more than girls. This means that when boys act out, they are in the wrong but when girls do, it's ok. See the double standard her? So basically, not only does the education system show double standards in behavior but also prejudices in grading. But when boys don't act out or when girls are the real class clowns or both of them act out, they will come up with more excuses.