But if they're invesigating the parent, how can they allow the parent to be there? It's likely that could put pressure on the kid to lie (assuming the parent IS abusive obviously)
It makes more sense to have the teacher there with the kid
The reason that the adult present is supposed to be a parent is because the parents are the adults who are legally responsible for representing the child's interests. When a child is at school, the school (and, by extension, its officials) are acting
in loco parentis, so they are tasked with acting in the interests of the child. Ethically, I do not see a problem with an informed teacher (or, better yet, a school psychologist) acting as a guardian for a child during questioning.