It's yet another of those intimations of mortality, and it's a bit of a shocker to realise that you may be teaching next to someone born 15 years after John Kennedy was assassinated, or horror of horrors, two years after you began teaching.
Whenever the TESS publishes First Appointments to help prepare newly-qualified teachers for the chalkface, I'm reminded what an impossible task that is. Methodology, subject skills, and familiarity with current policies can all help the young teacher approach the classroom with increased confidence, but what they can never do is foreshadow the pure unpredictability that makes teaching at once so enthralling and terrifying.
The scene in Gregory's Girl, where a penguin walking about the school is accepted as unremarkable by pupils and staff alike, puzzled many cinema viewers but for thoe of us who teach it was merely an accurate reflection of education's daily oddities.
In my first school, situated next to Edinburgh's Simpson's Maternity Hospital, the capital's parking problems meant it was not unusual for expectant fathers to park in our playground and then ask for the labour ward.
When I moved to Panmure House, off the Royal Mile, I was amazed that our reputation for helping disaffected pupils was so international, until it was explained to me that Adam Smith, the economist, had died at Panmure, and the large groups of camera-wielding Japanese were seeking his deathbed, rather than strategies for tackling school refusal.
Even last year, my smugness at controlling the back row lads in my fourth-year English class - despite having to teach them in a science lab - was shattered, when I found their compliance was 99 per cent due to the presence of a large snake in a glass tank a foot or so behind them.
I was back in the science department yesterday, but this time, I had to contend with Skippy the gerbil, who had crawled under his plastic feeding box and spent the double period trying to push it above his head like a demented weightlifter. The children were fascinated, and I was lost.
They don't tell you about that at Moray House . . .