Talk:Countermeasures/@comment-24801697-20151008181812/@comment-397235-20151008182235

The shunning doesn't have any weight outside of school, provided you're not at a school function, so somebody could've tried to clue Kouichi in outside of class. They state this specifically in the novel, but the only time it's ever brought up is in the anime, and since trying to do something about it apparently killed Ikuo, it scared everyone else into keeping quiet.

I don't know how they actually know about the Calamity, other than the rumor mill. It's specifically stated older kids ignore the ones in 3-3 so nobody's directly willing to discuss it. Some of the interludes in the manga and novel mention extended family members who've experienced the Calamity and talked about it, so that's the explanation I'd go with.