In Japan junior High is 3 years (7-9) and High School is 3 years (10-12). Tsuda started as a first year. Since Shino is one year ahead of Tsuda, and they've already had one Christmas together, this will be their second and last Christmas while both are in High School. And yes, this last year has gone glacially slow. Even if you count one strip per day, there are not enough days in the year!