Undoubtedly, those who have read manga or watched anime for quite some time will have determined that Japanese school systems are organized somewhat different than in native English speaking countries. The most marked difference is the fact that upper secondary education (high school) is not mandatory in Japan. Public education can be completed at 15 years of age. Despite that, most students do choose to attend upper secondary, and it is a rigorous process to study and take entrance exams for schools in high demand. Their families must save the money to pay for the education as well, since it is not publicly funded like in America.
If you are familiar with Nakamura’s Skip Beat!, main heroine Kyoko decides not to go to high school in order to work and support her best guy, Sho. She later resents him for depriving her of a “fun high school life”, and treasures getting to wear a high school uniform for a commercial shoot.
Japanese upper secondary schools consist of three grade levels, equivalent to American grades 10-12. I’ve noticed in different translations terms such as freshman and senior are used, but more commonly the class translations have been changed to first, second or third years.
In the published translation of Hatori’s Ouran High School Host Club, the character introductions include the students’ year of school.