Hi, Purple - I grouped this thread with our other parting song threads - the Parting songs thread has the widest variety. You may want to try a Digital Tradition Keyword Search (click) for parting - we have some 260 parting songs in our database. I guess you can't use "parting glass" songs for a school graduation, but I have to say that When First We Met is my current favorite parting song.
Good luck to you!
-Joe Offer-