Op MN has some of the most poe faced, joyless miserable fuckers on the planet on it, why did you ask! Just do it!
hyperbole, much?
In this country, we have universal, free education. This has a value beyond fucking rubies.
Sure it's only one day. The lights will be pretty. I'm sure they'll have a lovely time and pissing about with glitter is unlikely to compare.
This isn't the point.
The point is that every time you do this sort of thing, you're diminishing the overall idea that taking your education seriously is important. Just a tiny bit. Weeny tiny. Barely noticeable.
And your mates, or randoms on mumsnet, or whoever, are swayed by the idea just a little bit more.
People pick up on the inclination that school doesn't matter that much...it sort of snowballs a bit and then there's handwringing over getting teenagers to at least turn up for their exams, eh?
Not saying the line between going to see Santa, and a life doomed to failure is all that direct, by any means, but still- thin end of the wedge, eh?