Fruits Basket, Vol. 8 discussion

I noticed while reading through Volumes 1-7 that they go on vacation a lot for "Summer". But isn't there only 3 years of high school in Japan? And did Hatsuharu and Momiji join in the middle of Tohru's first year? The Chronology is very confusing up until around Volume 14. Can anyone help explain?

I Shall Explain.

In japan there are only 3 years of high school. their terms start in the spring during April and they only have a month of "Summer vacation. what you are talking about are the winter and Spring Vacations they dont show a lot of the school scenes in the books.