I had the huge good fortune of being taught history by Clare Marsland at Harrytown Convent in Cheshire. She was an outstanding teacher who arrived in my second year and taught me until A-level.
She was tiny, less than five feet tall, but she always wore very high heels, which were a cause of fascination for us girls.
When she came into a room, all she did was talk. The class would watch her with silent fascination. She never had any discipline problems because she treated us as adults. For the first two years she taught us like a lecturer would, and we just sat and listened. When we started our O-levels, the first lesson was devoted to how to take notes - a crucial skill that stayed with me.
She didn't make history exciting or turn it into vivid stories, but it was utterly engaging. There was always a sense of complexities within complexities and causes within causes.
Ms Marsland was subtly opposite to the spirit of the school. The place was ruled by sarcasm and we were constantly belittled. I felt wrong all the time. If you were not academically able, you were made to feel guilty, lazy, worthless or apathetic. If you were bright, they would bring you down and made sure you were suitably humble.
With most teachers I was frightened of making a mistake because they would make you suffer for it. Ms Marsland was different. She was never extravagant with praise, but I worked hard for just one word of praise.
I was unhappy at home. My stepfather didn't speak to me often except for explosions of rage. In those days, you never confided in an adult about your home life, so school was a chance to build a new set of relationships. It was important to look forward to spending time with someone outside home. Ms Marsland was that person.
When I came to secondary school, I was uncertain in every way. I was a working-class child from another town. I had had a poor primary education, I was behind and I stood out. From the moment Ms Marsland arrived, I began to find my feet and I started to flourish. She recognised that I could write. Instead of putting me down for being precocious, she encouraged me.
Her lessons made me realise the depth of the subject and stirred my intellectual curiosity. I had always had an almost emotional response to history since I was a small child. Ms Marsland's skill was to bring the past even nearer.
When I left school, I kept in touch with her sporadically. When my first novel, A Place of Greater Safety, about the French revolution, was published, she sent me a tremendous letter that is a treasure to me.
The first subject we tackled at O-level was the French revolution, and I realised that there was not a moment when I was writing the book when I wasn't thinking of Ms Marsland. I eventually lost touch with her. I've never felt able to tell her what a refuge her classroom was, and she had no idea of my chaotic family life, so she was one of those people who did good without realising it.
Clare Marsland is important to me in a lot of ways that I find hard to define. There are a few people in life who make you what you are. She was one of them for me.
Hilary Mantel won last year's Man Booker Prize for 'Wolf Hall', a fictionalised biography of Thomas Cromwell. She was talking to Hannah Frankel.