Two answers. One personal, and one observational:
At 26 I had lifetime employment, which gave me money and confidence, which I severely lacked in High School.
At the 5 year reunion, the jerks were still jerks, the stuck up girls were still stuck up. The nerds were still nerds, and only the jocks seemed to have been humbled. They were the first to change.
At the 15 year reunion, the jerks were still jerks, the stuck up girls were much more open, and human, and the nerds were still nerds, but making a good living.
At the 25 year reunion, the jerks were bitter jerks, the stuck up girls were attracted to the nerds, who had made millions.