A colleague unearthed a faded staff photograph taken many Christmases ago. What struck me most was that all the nuns wore wimples. I remembered a nun who not only wore a wimple, but who must surely be worthy of the prize for the most imaginative classroom resource material ever devised.

Sister Kieran decided to give presents to her firstclass pupils three days before the Christmas holidays of 1950. She gave me a bright red Charlie Chaplin-style tash with a splash of glue to keep it suspended under my nose.

"But Charlie Chaplin's tash is black, Sister," I protested. "Ah," said she, "every colour looks black or white on the cinema screen." That statement satisfied me and silenced the taunts of my envious classmates. For three days, I sported the red tash and even wore it to bed. Sister Kieran replaced the glue each day. I wondered why the other nuns in the convent beamed so benignly each time they spotted me wearing it - nuns I had never seen before emerged from nooks and crannies to view and admire the tash.

I thought they smiled because they had the privilege of having a potential Hollywood child prodigy in their school.

On the day we got holidays, I decided to live as well as look the part. I mimicked the Charlie Chaplin walk all the way to school, wore my father's Sunday hat and brandished my grandmother's walking stick. The girls in my class vied for my attention; I felt that silver screen stardom could but be a few short months away. The slow dawning of a shared class epiphany began when no one stood up for prayers as Sister Kieran breezed into the classroom in her usual brisk and jolly manner.

The girls and boys froze in their seats, stared first at her and then at me. Sister Kieran followed their stares from her face to mine. Instinctively she put her hands to her face.

But it was too late. The entire class had seen the strands of bright red hair streaming down her face from beneath her starched wimple. A dramatic epiphany for every pupil: nuns had hair. But I was the one wearing what were certainly the clippings of her most recent haircut. It was an event, as Yeats put it, "that changed some childish day to tragedy". Later that morning, Sister Kieran gave me a gleaming new Dinky car for being the best pupil in the class. My smashed ego massaged, my classmates' envy excited again, I was happy to forgive and forget. A photograph that was once so commonplace is now a curiosity. I thought of showing it to my first-year class, but the sight of the clothes and hairstyles of the lay teachers in the photograph would have surely generated a riot rather than a ramble down memory lane.