The best teacher I ever had, since you ask, was not one of the obvious ones.

I had some cracking teachers in college and university - Sylla (Spanish), Theo (English), Rosie (Sociolinguistics and Quechua) - in their own ways, each of them inspired me to learn, extending the student-teacher relationship into friendship (whether that meant eating chocolate fondue at their flat or lending favourite books and urging me to read them) and I have to thank them.

But the best teacher I ever had was not my favourite. She was a woman called Ms Stacke and she was not an easy person to like. At all.

Ms Stacke (I think her first name may have been Elizabeth) taught me geography for five years in secondary school. She had icy blue eyes, and white blonde hair pulled up in a tight chignon at the back of her head. She was probably late forties, early fifties, and she was so difficult to impress. It drove me crazy.

Without sounding big-headed, I was sort of used to being able to sail through classes on flukey essays and general knowledge. I didn’t feel particularly challenged by any of my GCSE subjects (except maybe physics, but that’s another story) and the whole school experience bored me. I did a few exams early, and yawned through the rest.

Ms Stacke, however, was hard to please. However good my essays, however flawless my projects and presentations, she always wanted more. I remember getting 97% in my GCSE Geography mock exam, and she badgered me about the other 3%, telling me I’d made a stupid mistake. She never once let her guard down, never once made concessions for anything or anyone, always expected more, always pushed me harder.

She’d travelled a lot, and her eyes lit up when she talked about the San Andreas fault, Crater Lake, Mount St Helens. She made me want to travel more, to understand how geography applied in the real world. She refused to allow me to be satisfied with my classroom, my city, my life. She made me itchy for more knowledge, more experience.

When I won the scholarship to study in Canada, she was over the moon, though she didn’t let on until a whole year later. I whizzed through my GCSEs, acing geography with the only perfect score in the country. Still she never said a word. Not “well done.” Not “good for you.” Nothing. I clenched my fists and left for Canada, where there was no geography syllabus, and I was forced to take Anthropology instead.

A few months into my time there, I sent Ms Stacke a postcard of the San Andreas fault, from a trip there. I’d seen geography in action, and I wanted to thank her for making me seek out the knowledge and the experience. She sent back a postcard from Bournemouth and a stack of maps of Canada, which she’d been saving for me. She’d taken early retirement. She’d left London. She was proud of me. Goodbye.

I have seldom felt so incredibly proud as I did then.