Girls Are Good at English, Boys Are Good At Math

Why is it that males are thought of as being good at math and science, while females are supposed to be good at English and Social Studies? It's become such a part of the learning structure; I'm beginning to think educators plan it that way. Everyone, as a matter of fact, is trying to make us feel that way as far as I'm concerned.
How many times have you heard someone say that girls tend to be or are good at English and Social Studies, while boys are good at math? Obviously, in some cases, this is true. But is it really just gender?
No. There are other factors. Do you like the teacher, for one thing? Are you even interested in the class? When you're interested in what you're learning, you retain 30% of the lesson. When uninterested, you only remember 10% of the lesson. If you have a teacher who can keep your interest, that makes a difference.
Maybe this myth is so engraved in our minds that we just believe it. What if, subconsciously, Abbey puts more effort in English because she thinks that girls do better in English? She figures that because she's a girl, she'll do better in English than in Math, because Mom's been saying so for years. On the other hand, if Johnny were never told that boys were better at math than they were at English, what would he be better at? Is he going to subconsciously put more effort forth for math? Most likely not.
So, where did this story come from? Did it come about because boys received better instruction in math? Do teachers feel that males are more likely to need math and girls are more likely to need English? If that's the case, then why do they feel that way?
It's sexist, but not just for females. If a class is centered more for males than for females, it's sexist, and vice versa.

* I realize that this essay asks a lot of questions, but I was just reading about Sigmund Freud and began pondering this, because of some of his viewpoints on women. Anyway, please review.