I've been hearing since grade school that standing straight improves brain activity, that you will be able to think clearer, faster, better, etc. Mostly, it's teachers who say that, but I have yet to find any scientific proof that it's how it all works.
Pupils are expected to stand up when answering teacher's question. Also, talking to teacher while sitting is considered bad tone or outright rude. In school students are supposed to speak to teachers while standing unless the teacher specifically allows the student to sit while answering.
I suspect this "standing up makes you think better" thing was originally supposed to encourage etiquette, so as not to come off as rude when talking to teachers and seniors while sitting.
Also this may have started as a way to teach children that sitting too much can be harmful. This I can agree with, as it's scientifically proven that people who don't move around enough may suffer from various illnesses.
I've talked to my classmates when I was still in school and they mostly disagreed with that statement. They thought that if they were to stand for too long, eventually they would become too tired of standing to focus on the task at hand, which would be the exact opposite of the expected result. Besides, being the only one (or one of the few) students standing would look like an attempt to show off, so then we decided it would harm our reputation and didn't do it, even though some teachers said they encourage standing up during their classes.
Does standing up instead of sitting allow you to think better, or is it a school myth?