The autumnal chill has had its usual effect on our pupils - they're permanently starving.
"Can you stop eating in the library, please?" I ask.
"I'm not eating, Miss," Tom mumbles unconvincingly through bulging cheeks.
"Yes, you are," I say. "You're eating a sausage roll, I just saw you. Can you eat it somewhere else, please?"
Tom looks at me for a moment, then squeezes the sausage roll into his fist and stuffs it rapidly into the pocket of his suit jacket. I consider the consequences for whoever is in charge of cleaning his clothes. Doubtless Tom's response, when challenged, will be: "She told me to, the librarian."
I can almost hear the sixth-formers, slumped at their tea tables at home, reeling off the extensive research tasks they like to think they've achieved that day in the library. But, I wonder, do they mention the diverting game of hide and seek between the reference shelves, or the invigorating - and rather loud - discussion with the chief librarian about suitable websites. Not to mention being banned from the library for the morning, after persistently making their friends' mobiles ring ... somehow I doubt it.
As a parent, I know what an uphill struggle it can be to elicit from your offspring what they have done at school that day.
"Oh, just stuff, the usual," they sigh from the depths of the sofa they have flung themselves on in a seamless movement from the front door.
"And lunch?" You want to know they have taken full advantage of the energy-giving, two-course meal you are paying for.
"Can't remember, but it was revolting. I got some chocolate after."
"Great. So all you've had all day is some chocolate ... But wait, what's this in your jacket pocket? Oh yuk, what is it, for goodness sake? And why is it in here?"
"I was so hungry, Mum, I was fainting and I was just trying to eat a bit of sausage roll - you always say I need more meat - when the librarian said I had to put it away."
The rule about not eating or drinking is notoriously difficult to enforce, of course, and does often seem unreasonable. As with everything, a modicum of discretion helps. If they're just popping a jelly bean in their mouth, fine, but if they're covering the desk with flakes of pastry from, for the sake of argument, a sausage roll, then not fine. Even so, I often spot a mass of goo and crumbs beneath the chair when someone walks out, so I must be missing a few jam doughnuts.
It's all about calories - teenagers seem to need unending supplies to prevent their energy levels from slumping into a dejected heap inside them. And I do sympathise, I really do.
"You're eating in the library, Miss!"
"No, I'm not," I lie instinctively.
"Yes you are, I just saw you with an almond croissant and you've got crumbs down your shirt."
Claudia Court works in the library of a London secondary school.