It's a tradition in my classes that we say good-bye to anyone who is moving by letting them know how much they have been appreciated. My students always ask to make sure I don't forget to do that "appreciation thing." I love that middle school students are asking to say nice things about each other!
This is how we do it. Everyone in the class stands in a circle. I have an inflatable globe that we pass around for the activity. Only the person with "the world in their hands" is allowed to speak. Each person completes this phrase about the student who is moving "I appreciate (name) because ..." Sometimes even the most unlikely students will share the most sincere and thoughtful appreciations or perhaps shed a few tears. These are some of the times I feel the most pride in my classes. I love to see them show kindness to each other.
Some students have a harder time with this than others because it does not come naturally to them. I usually give the class a minute of silence before passing the globe so they can collect their thoughts. I also explain how it would be rude to not have anything to say, so everyone must think of something. I encourage them to stay away from general statements like "He's a good friend." and instead say something about what makes the person a good friend.
I thought of this idea after attending a training for Tribes Learning Communities several years ago. Tribes has been around for decades, but it has good ideas to build a positive classroom environment. I've used the book a lot. If you'd like to check it out, click on the image of the book cover for purchase information.