This is hilarious! I’ll admit to being quite a strict parent (a whole lot stricter than most of my 14yr old DS’s friends’ parents anyway) but I still find it funny.
As for the PP saying that maybe it’s a difference between English and Scottish schools and it wouldn’t happen in Scotland - I live in Scotland and I can totally see this happening.
My DS’s school is a riot of people. I have had the (unfortunate?!) pleasure of being in the school at various points in the day as I run a lunchtime club in the library and have been in classes during class time when I have needed to liaise with teachers about things. Often the kids are sitting in groups, not specifically at a set desk and DS informs me that they only have set desks for their practical subjects (Home Ec, Science, DT, Computing). The rest of the subjects they can sit where they like so a new student wouldn’t stand out.
We also live in a fairly transient city where people move all the time and it wouldn’t be uncommon at all for people to switch schools or for a new child to randomly appear.
Yes - you have to register before starting at a school, but I know of pupils who have registered on a Friday afternoon and started on the Monday morning. Data forms/health forms/school trip permission forms are usually done once term has already started so it would be perfectly possible for a student to be in school without being on the register as the paperwork hadn’t been updated. (We are now in the 5th week of term and DS says that plenty of people still haven’t handed back their data envelopes that were handed out in the first week of term. The kids are chased up with a general “please remember to return your brown envelopes” in form time each morning, but the kids still carry on with their day as normal.)
The only reason this would be unlikely to have happened at DS’s school on the first day is because they move up to the new year group in June, so while there are new starts in August - they do stand out because the class is already established with the new teacher as they’ve had them for a month already. (Still not impossible though!)
For what it’s worth I was also volunteering last week in my DD’s primary school for maths week and in one of the classes the DHT was taking the register at the start of the day and it was a paper copy of last year’s register - several kids have left and there were a few new starts so she was having to try and remember who was supposed to be there and who wasn’t. This is in a relatively small primary (2 classes per year group) and with primary pupils you’d think they would be more hot on “safeguarding”!