My experience in the US has been that girls work harder than boys and thus get better grades on average. I did have a bull-**** teacher once who fawned on the girls and hated the guys (particularly me) but she's an outlier. She once accused my friend of plagiarism because he used the word "beguiled" in an essay; I suppose it wasn't possible in her world for him to know the word or to have access to a dictionary or thesaurus. I was certainly arrogant in high school, though introverted, yet if anything I received better treatment from many female teachers. The same was true for me in college.