Every now and then, as the parent of a school-age child, the yawning gap between how your home life works and how school staff think that it works becomes painfully apparent.

The fact is that, however delighted you are with your child’s school, its implied assumption that there’s an adult at home who can drop everything at short notice to contribute to extracurricular activities is a rather frustrating one.

There are a number of school events that cause logistical difficulties and hair-tearing for families, but the proliferation of school dressing-up days is a particular thorn in the side. At the start of this month, grumbling about the expectation that children turn up at school in costume was dialled up from a background murmur to a shout in advance of this year’s World Book Day: the annual celebration of causing your parents extreme stress by suddenly demanding a Charlie Bucket ensemble at 7pm the day before it’s needed.

Of course, it’s difficult to object to this without sounding like an oddball who is deeply hostile to literacy. What sort of parent wouldn’t be keen to nurture a child’s bibliophilia?

Too little time

But many parents are simply not convinced that panic-buying a shiny nylon costume for £20 is a particularly effective way of persuading a child to give Mr Gum a go. (And before you ask: no, we can’t make it from things we’ve already got at home.)

Some children aren’t that keen on dressing up, and spend the whole day feeling uncomfortable. And plenty of parents are just fed up with schools’ apparent belief that most homes have dressing-up boxes that would be the envy of the Old Vic and are easily able to accommodate the annual demand for nativity costumes, Easter bonnets, French accessories, Victorian knickerbockers and Comic Relief-themed polka dots (always one size larger, of course). Christmas jumpers seem to be the newest addition to the interminable list, sending clench-jawed parents down to Primark at a time of year when the extra expense is especially unwelcome.

In the end - as with complex homework projects necessitating adult involvement - it’s difficult to escape the impression that this is thanks to unexamined assumptions about the availability of parents’ (let’s say mothers’) time, and/or spare cash. These days, household economics demand that most families have two parents in paid work; single parents are often working and undertaking all domestic duties by themselves. Parents are usually happy to spend time helping their children with reading, but using what might be their only spare hour of the day to arrange yet another costume can be another thing altogether, especially when the benefits are so unclear.

Of course, there are children who love dressing up - and even parents who love designing the costumes - but for the sake of everyone’s blood pressure, it would be constructive if costume days could be made explicitly optional. I suspect that the Mumsnet user’s daughter who “had to go as Hermione Granger four years running” would be inclined to agree.

Justine Roberts is founder and chief executive of Mumsnet. See mumsnet.com/talk/education @justine_roberts