This is a end of year activity I do with my 8th graders. They use the handouts and write letters to themselves. I keep the letters until the students are Seniors. Toward the end of Senior year, I pass out their letters or mail them to them. Students love this! They love looking back at how they were just only 4 years ago. They always come to me after and tell me the funny things they wrote. I never read their letters, unless they want me to. This is supposed to be personal and private for them.
I bring business size envelopes. After students finish their letters, we fold them up, seal them, and put their information on the envelope. I usually also get them to write their phone numbers and parents numbers on a sheet of paper, in case the student moves, I can call and get their address to mail it to them.
You can make this assignment/activity as long or as short as you want it to be. We are on block schedule (students have me back-to-back for two class periods). I usually give two days (4 class periods total) for them to work on it.