Miss Gummer taught me English at Oxford High School for Girls in the 1950s when it was a grammar. She was a fascinating person: she had studied at the Royal Academy of Dramatic Art and had also been a nun.
I don't know why and when she left the convent - or why and when she left the stage - but the theatre was a passionate part of her existence and something we shared. She would arrange class trips for us to see plays in London.
Miss Gummer looked fabulous. She had a leonine head of grey hair swept back from her face, blazing grey eyes and a rather waxen complexion that made her look like a saint.
I was extremely naughty at school but never in her class - I didn't want to miss anything. Miss Gummer had a gift of making literature as thrilling to her students as it was to her.
As head of English, it was her job to direct the school play. She wasn't the first to notice I was good at acting (I always say I tap-danced out of the womb) but she harnessed my energy. I was a real show-off, but I was fabulous if I was focused; Miss Gummer saw that. She cast me as Brutus in Julius Caesar and I played Gertrude in a wonderful production of Hamlet.
She also encouraged me to enter the public speaking competition, which I won year after year. Public speaking is an important part of my life now, as I get paid for it. So I have Miss Gummer to thank for that.
She was one of three giants of my school life, all of whom were in the English department. Right at the beginning, I had Miss Bartholomew (whose passion for Shakespeare was so great that she literally foamed at the mouth), Miss Gummer and later Miss Gilbert.
Because they loved words so much, I loved words. Thanks to them, I studied English at university and that really was the start of my life.
I was the form wag at school and always tried to make people laugh. If a teacher had no discipline, I'd think: "I'm going to have some fun here."
Once I borrowed my mother's fur coat and high heels, knocked on the door of a French class, went in, put on a French accent and claimed to be a mother inspecting the school for my daughter. The teacher, Miss Willetts, said: "Don't be silly, Miriam, sit down." But I carried on in character and she was trying not to laugh.
Another time, I got inside the pommel horse in the gym. My classmates could see me through the handles but the gym mistress, poor love, was quite unaware of what was going on and found it peculiar that the horse seemed to move.
Many years later a teacher said to me: "You were naughty, Miriam, but you were never wicked." That pleased me.
Miss Gummer was quite a serious person but even she enjoyed my jokes and my energy. I kept in touch with her until she died in 1980. We would write letters and meet for tea in Oxford occasionally. I will never forget her - she was a powerful influence on me.
I loved school. I was an only child, so I very much depended on the companionship I found there. My two best friends from that time are still my friends today.
In 2009, I went back to open some new buildings at Oxford High School. They named a studio space after me. They had wanted to name it after another old girl - the actress Maggie Smith - but she declined, so they asked me instead.
Miriam Margolyes is supporting National Doodle Day, which raises money for Epilepsy Action. For more information, visit www.epilepsy.org.uk or www.nationaldoodleday.org.uk. She was speaking to Kate Bohdanowicz.
Born: 18 May 1941, Oxford, England
Education: Oxford High School for Girls; Newnham College, Cambridge
Career: Bafta award-winning actress and voice artist, whose roles include Mrs Mingott in The Age of Innocence, Professor Sprout in the Harry Potter films and 23 different characters in her solo show Dickens' Women.