This happy and woefully rare coincidence always provides a great opportunity for reminiscent whooping and giggling about Reverende M re, white gloves, dictee, learning Fables de la Fontaine by heart, and doing danse eurythmique in white tunics like a row of chubby little Isadora Duncans.
Fellow inmates are the only people who will ever believe that they actually used to serve beer to us at lunch, at nine years old: a litre bottle between a table of eight. And sometimes I even meet someone who, like me, used to get nul points on her report for "maintien" or deportment:
"Elisabeth se tient tr s mal" wrote the Maitresse, damningly.
But on this occasion, as it happened, our conversation turned to the subject of the tablier, or overall, worn by all good little French bourgeoise schoolgirls - and smaller boys - at that period, and which endures in some Continental schools even today. It was universal. Until you were in the senior school you wore a full tablier, a sort of chic, good-quality cotton housecoat, in our case sky-blue with smart navy-and-white pinstripes at collar and cuffs.
It was buttoned and belted, covered everything from neck to knee, and was not at all uncomfortable. even in high summer, as you could just wear your blouse and skirt beneath it.
The tablier was the front line of defence against ink, pen, paint, food spills, crumbs from our mid-morning baguette, dribble from the school rabbits, and exhilaratingly muddy playground games like ballon prisonnier, with which we blew off steam in the walled garden at break.
We only took them off for gym (or eurythmic dancing) and for formal occasions like chapel, when we donned white gloves and veils to add to the sense of ceremony. Your mother had to wash your tablier once or twice a week, depending on your habits, but that was nowhere near as much of a nuisance as washing or cleaning school skirts and sweaters.
When you became senior in the school, upward of 14 years old, it was replaced by a dark blue, thick cotton pinafore, a simple sleeveless over-the-head job with ties at the side.
Remembering these details, we wondered why on earth schoolchildren don't wear tabliers here and now. Think of all the problems it would solve at a stroke.
Schools which don't have uniform would have their pupils vaguely homogenised in school hours, with minimal opportunity for designer one-upmanship and bragging.
Schools with uniform would find the children less tiresomely insistent on "customising" it by turning up the skirt, leaving the shirt hanging out etc, because there would be no point once you got your working overall on.
Catwalk behaviour would move back to where it belongs, after school hours.
Parents would be spared the awful task of maintaining school sweaters - which could therefore be made of less offensively cheap wool - and nobody would have to contemplate the depressingly shiny seats of budget schoolwear which has been polished on hard seats all day.
The growing problem of pubescent girls decked out in bare-bellied slutwear with visible thongs would be neatly knocked on the head because the tablier would cover all pierced navels and bum cleavages with workmanlike, practical sky-blue cotton.
And all this might be resisted rather less than you might think. The overall, after all, would be seen not as a horrid imposition of schooly values (like the ghastly grey A-line skirt) but as something practical, a reminder that the school day is long and varied and tough and grimy.
The tablier provided, as I remember it, a sense that it was OK to work a bit messily or scruff around in the playground, because that was the way it was when you were a schoolchild.
Rather than limiting children, it freed them. It was, in fact, the opposite of a ridiculous note we once got back from the worst school we ever used, which said primly: "We expect our pupils to dress and present themselves at all times as if for interview."
Damn ridiculous: what, in that case, is left for interview? And why should a busy Year 9, scuttling from lab to drama with an armful of books, be expected to worry all the time about interview-standard neatness?
No, it is decided. When I am in charge of things, there will be tabliers issued at all schools. It might be nice if the teachers wore them too, in a contrasting colour. Heads and deputies, perhaps, could have epaulets. Or special belts. Oh go on, think about it. I'll let you off the white gloves, for now.