I have a few suggestions if your character is in grammar school - my daughter's class has had three kids leave. Each time, the teacher sent my daughter home with a blank letter, for her to write the departing kid, and a place to attach a photo. They also do a regular party - someone brings in a treat or two, and drinks, and they just kind of hang out at the end of the day.
Anything older, though, and I'm not much help - sorry 'bout that.