My son went through a phase of pooing himself, it hit when my mother was seriously ill and I just figured that it was attention seeking. We got some advice and working with him and at home at least it's no longer an issue.
But he still does it at kindergarten. And they are fed up with it and are actually getting really nasty.
They are suggesting it must be something medical (doctor disagrees) I suspect that since they have increased the class size by 60% they simply don't have time to notice.