For those who have no connection with schools, it basically means sending your offspring off to school dressed as some ‘favourite character’ from a book.
I have a very clear memory of attending a school assembly one year – my daughter was working, so I was happy to go.
As we waited patiently to get into the hall, an infant class passed with no fewer than eight Queen Elsas from the Disney film ‘Frozen’.
There were also at least 20 Batmans (Batmen?) and about 40 Iron Mans (Iron Men?). It may have been more, I lost count.
Now, you may argue that Frozen is based on Hans Christian Anderson’s famous tale The Snow Queen, although personally I think you’d be skating on thin ice.
And, of course, if you want to encourage reluctant readers, comics are brilliant, so Batman and Iron Man, you can stay. Yes, all of you.
There were always creative souls who’d diligently make their own costumes –I was a big fan of the mum who dressed her kids up as a page from the Argos catalogue – but for most parents, time is precious and in short supply.
And, to be fair, the choice has grown remarkably.
In recent years, the supermarkets have woken up – with a kerching – to the demand from tortured parents who need another item on the to do list about as much as they need an extra big toe.
So, for around £12 or so, you can wave them off everyone’s favourite boy wizard, Harry Potter; or Fantastic Mr Fox; or maybe The Cat in the Hat.
No-one is forcing parents to buy costumes so that’s not my problem. My big gripe is that I’m not sure it’s the best way to make children want to read.
Reading with a child should be about relaxation – for me, it was always a special time at the end of the day, perfect to help the kids wind down at the end of a busy day.
In a world full of smartphones, tablets, Playstations and XBoxes, I firmly believe we need books and stories more than ever.
So, if the rush to get a costume means you have to skip the bedtime story, forget it.
It’s the story that matters.
Of course, if you’re really bothered, they can always go as something out the Argos catalogue... or Queen Elsa.