That's true we don't know if she was in school before being brought into the series there is no real age given for her either, it's up for speculation.
I was just basing it on the fact that she was a freshman in the infinity arc in the manga.
In the anime I don't think we ever even see her as a student.
2 years in the manga, she may still be going to school, but she has to have a degree in order to be a school nurse and not just a student and most nursing courses I know require 4 or more years, or 2 years in accelerated courses.
If she is privy to future knowledge as some speculate, she could have been going to school for nursing the same time she was a freshmen majoring in physics. Some schools allow multiple majors.
Rei hasn't really changed position in either of my lists because I find her to be good at school and good at her studious performance.
I base my ideas on the manga that clarified her position as school mkre than the anime.
She was admired by students and teachers for her work, her attitude, her grace and the list goes on.
While not any more intelligent than Minako, Mailto and Usagi, in my opinion, she is a hard worker and she not only enjoys school, she adores her own school and being a role model for her fellow students.
And I agree with Small Lady on the schools part. In Japan, high school is hard to get into, like a regular state college in the US would be.
I don't really connect the different in schools as a way of defining who is good at school or performs better otherwise we can't include grade schooler Chibiusa.
Advanced and extra classes would count more to me.