There is certainly something to be said for having an official goodbye speech or party. As I've prepared to go home, I've noticed that it makes a huge difference for how I feel when I leave a school for the last time if I'm able to feel as if I did a proper farewell.
The first example is a school that I always loved going to, but where I had my last day in May before my family visited. I wasn't even thinking about leaving and no one else realized it was my last day so it was just another workday to me and everyone else. For the students there, and for myself, I just kind of "disappeared" from their lives with no end, no last chance for a picture or to say goodbye. It's a book with a cliffhanger and no sequel.
The other example is at a smaller school near Kitami. There are about 120 students, and I taught all of them almost every time I visited. On this particular day, I visited each class, took a class photo, enjoyed one last game, said some goodbye speeches, and enjoyed the English Conversation class party they threw for me (1 student + all the English teachers = great fun). I was asked to wait 30 minutes after school, and then I was presented with a wonderful homemade yearbook:
Every student is pictured in the yearbook, and everyone wrote wonderful little notes to me. It's a full book of student photos, pictures of me teaching, and class photos. Here's a few samples of the inside of the book: