This is actually a very interesting and thought provoking question! I'm in year 12, so I'm currently coming to terms with the fact that I only have 3 and a half weeks left of school EVER. I don't know if I'm more attached to my specific high school, or just the idea of going to school in general, because its been such a major part of my life for 13 years.
I do really like my highschool, it seems to have a positive, encouraging atmosphere and I have always enjoyed school (more or less). I love the senior learning centre we have, which is just for year 11 and 12, because it is a quiet place to study or to hang out in study periods, and the main teacher there is very approachable and supportive. I have a small but great group of friends, and have a friendly relationship with a lot of other people in my year. I am also vice captain so I am fairly involved in the school.
I think I will miss the support and structure of school, and the close relationship with some of my teachers which I think it will be harder to develop in uni. I'll also miss the friends and forced socialisation (I'm hopeless at organising social things outside of school), I love that there are people I talk to in classes and other situations who I would never usually be close friends with.
I have a younger sister so I will definitely be hearing about the school for the next few years, and after that I guess we'll see what happens.
So yeah I think I am fairly attached to my highschool, I'll definitely be one of the ones getting teary at graduation! It feels like it's crept up so suddenly, it will be such a weird feeling walking out of school (officially) for the last time.