Shiritsu Sei Cattlya Shougakkou

I resigned from St.Cattlya Kindergarten because I want to teach at a High School. One day, I received a letter from Yamasaki-sensei. Oh, is that a love letter? But why the clues at the letter guide me to the St. Cattlya Primary? Oh,NO! I have to teach my previous students again. Where's those young high school girls I always dreamed of?