At the school I attended, a pupils path through the establishment was pre-ordained.
Everyone was expected to sit 9 O-levels. (Everyone did).
Everyone was expected to go onto the sixth form. (Everyone did, except for one rebel who left to join the police force).
Everyone was expected to sit three A-levels. (Everyone did).
Everyone was expected to apply for entry into higher education. (Everyone did).
Everyone was expected to actually go onto higher education. (To the best of my knowledge, everyone did).
So when, at the end of the sixth form, we were all invited to join the Old Boys' Association, I simply assumed that everyone would. Everything else connected with the school had happened automatically, so I just saw it as part of the plan. I liked the idea of being able to keep in touch with others from my school anyway, so I dug deep in my pocket to pay for a life-time subscription.
A few months later I received my first communication from the Old Boys' Association. It was a circular to say that, as only one member of my year group (me!) had joined the association that year, the committee had decided that it was time to wind the association up. (That's all I ever got for forking out for a lifetime membership!)
So I've got the feeling that there probably aren't that many people from my year group who would be interested in attending a reunion!