Why did noone from the first years know about the sorting ceremony?

In the first book just before the sorting ceremony everyone was quite terrified noone had an idea what is going to follow (even Ron who came from a wizzarding family). Why is that?

The ceremony itself is not a secret since most of the wizzards in England went through it. Even if there is a unofficial rule not to talk about it, at least some of the kids would have heard about it and spread the news.