After graduation, you won't believe how fast 10, 15, 20 or more years go by. Before you know it, there will likely be a high school reunion. Depending on the dedication of your classmates, there may be a reunion at any significant date. Some people try to organize for 10, 15, 20, 25, etc years. This seems a little excessive. Most classes get by with every 10 years. Some classes seem to have a reunion at major points such as 25 and 50 years only. There is no set schedule, of course.
When it is time for a high school reunion, the organizing committee gets active, usually 6 months or more in advance. These people tend to be the organizers from the graduation committee, yearbook staff or other dedicated people from your time in school. This is not an absolute. Some people get involved in reunions even though they seemed to take no interest in school. Regardless, the job of the high school reunion organizing committee is very complex and they deserve top marks for their efforts.
A lot can happen in your life during the years since graduation. You may start a career, go to college, move and have a family. This makes it difficult for the reunion committee to find you. They usually try to connect to your last known address, that of your parents. In 10+ years, however, they may have gone through changes as well. The reunion committee expects to reach 50% of the graduation class via the old address, at best. The others get missing status. Alternate means of contact are taken to find these people and notify them of the upcoming high school reunion. There may be a small ad in the local paper or on the local radio station. With the Internet, the committee will likely set up a blog. After the event, there may be further communications that lets people keep contact.
Some people may not want to attend their high school reunion. They may have memories from high school that they would rather forget. Perhaps a particular person will be in attendance. Maybe they are concerned about the changes that time has made to their bodies. All of these reasons are quite unfortunate and generally unfounded. If you are comfortable with yourself, you should make an effort to go to the reunion. You will have a good time reuniting. As for the memories, you ignored them for 10 or more years, what's another couple of hours?
Since your graduating class will come together for the first time in many years, it gives you the chance to relive some good times. As well, you can finally connect with people that you may have missed for years. Depending on the class, there may be a web site set up or a Facebook page. That may let you get your friends' email addresses so that you can keep in better contact with them in the future. It is amazing that after graduation, many people just drift apart, people who were extremely close in school. Now with the Internet, it can be possible to maintain these connections. Even a quick posting on email or Facebook goes a long way to keeping these friends in your life.
It can be amazing to see what has changed between graduation and your high school reunion. People change, of course. Look at your own changes in that time. Besides the obvious changes in appearance, your life has brought you a lot of change. The same goes for your classmates. You all have careers, families, advanced education or at least a lot more experience. In time, your class will provide the leaders of society. This is a natural progression. While you are living in the years after high school, you may lose track of your roots. Going back to your high school reunion gives you a chance to re-visit a part of your past. You get to see friends that you likely haven't seen in years. You can learn a little about the changes in their lives. At the end of the high school reunion proceedings, you can go back to your life with another small experience to remember. You can choose to keep in touch with some of your classmates or not. Try not to skip your reunion if at all possible.