"Have you tried lost property?"
That question buys you time. But not much. How often does a child come bounding back to you shouting with joy that their brand new, clearly named mobile phone was in there all along?
Lost property is weird - a damp, smelly mystery that sucks things into itself. Its real name is The Swamp of Non-Being.
To their owners, these objects have ceased to exist. Yet how do you lose your trousers and not know it? And here's someone's passport - at least that's named.
The Swamp of Non-Being is full of things such as purple iPods - things that make everyone except the owner go, "Ooh, I want that!"
While those scientists in Geneva are busy repairing the Large Hadron Collider, one of them should look in the lost property cupboard of their local school. I wouldn't be surprised if they found the Higgs boson squashed between a school blazer and a ham sandwich.
After all, during the daft fuss about whether the LHC might destroy the world, it was explained that there was a tiny chance that it might produce "a minuscule black hole" that would "decay immediately". That's the best description of lost property I've ever read.
Pupils react to losing things differently from teachers because, unlike us, they didn't pay for the stuff themselves. If I bought a new jumper on Monday and lost it on Tuesday, I wouldn't stop looking for it. But then I can't just go home and tell my parents that someone must have stolen it, so can I have another one, please?
There is more to it than money, though. In matters of loss, scale is everything. When a pupil says to a teacher, "I've lost my pen," it is hard for the teacher to care if he or she is thinking, "I've lost my house". But it's worth remembering that many of our pupils are dealing with loss for the first time.
A friend of mine still remembers the day she came home from school and was told that her puppy was dead. Her father poured her a stiff whisky, "But I was in shock and I didn't feel it. That was my first loss," she said.
Adults have learnt to live and laugh after losing jobs and loves. But children still have to deal with the first loss - searing, stupefying - that seems to have nothing beyond it.
We may be more used to loss than our pupils. But do we always take better care of our things when we've grown up? Banks lose money; governments lose data. And here is just some of the lost property left on London's public transport: a stuffed eagle, a wedding dress, a blow-up sex doll, a lawnmower, a judge's gown, a human skull, several false legs, a jar of bull's sperm, three dead bats in a box, a funeral urn (with ashes) and a four-metre boat.
As we get older, we do get a bit better at dealing with loss. Unfortunately, we also get even better at losing things.
Catherine Paver, Writer and part-time English teacher.