The most obvious one to me is violations of FERPA rules and posting private information/pictures of my kids in a public forum.
1) OP stated they were "notifications and polls", neither of which would contain private information or pictures.
2) You make the assumption that the school does not have a private / protected group that is used for verifying group members and protecting content from non-members.
I do make that assumption because your average staff member that would manage something like that, would do the easy path of default settings (which are probably public).