American high schools use the grade system and are actually 4 year institutions, going from grade 9 to 12, and are sometimes referred to as freshman (9th grade), sophomore (10th), junior (11th), and senior (12th).  (I know a lot of countries following the British system like Japan and Taiwan have three year high schools, so America is slightly unusual in that regard.  Feel free to change some of the character's ages if you would like) That being said, I'll probably stick Shelley in the 9th grade which will add to the fact that she doesn't know Hoenhime.