You identify if they actually are the person who is permitted to have access to the child. That paperwork, which is submitted upon enrollment is signed, stating who has the permission for access to the child. A phone call can be received by anyone in the house - and so, whoever “shows up” is not necessarily the person who has permission to access the child.
Bingo. My son attends a private school and they have similar security protocols.
When parents divorce, as so many do these days, and are battling for custody of the child, abductions from school by one of the parents is a real problem a school has to deal with.
So, according to the one person who responded to the article by saying the mother was always a problem and made a spectacle of herself (not that exact wording), it must have been well known in the school that she was on the paperwork to have access to the child...so your arguement is mute.