A Certain Slant of Light

I was actually surprised by the psychological credibility of the whole thing. As you say, poisoning is an extreme example, but I think the kind of dynamic portrayed is something that really happens at that age (or at any age, really, but I think it's often most extreme around middle school), where no one wants to be the one who goes against the group by saying "How about we don't do that?" even though secretly most of the group doesn't want to do that. The ringleader and the intensely uncomfortable followers who would really rather not.