I'm not sure how much I would have enjoyed my time at Tonbridge School in Kent had it not been for my English master, Jonathan Smith. He was one of those magical teachers who could spot a kid in trouble and know the right thing to say to him. I owe him a tremendous amount.
Not that I was miserable at Tonbridge, but in some ways I did feel out of my element there. For starters, unlike most of the other boys, I was a scholarship pupil - the son of two teachers rather than wealthy parents. And on top of that, while I was pretty good on the academic front, the sporty culture of the school wasn't my bag.
As it happens, I love all sport now. But being told that I must play sport brought out the worst in me. You would either find me behind the proverbial bike shed smoking a cigarette or going off to do a school play. But then, from the word go I had always been the idiot who wanted to get up on stage and perform.
It is thanks to this that I first encountered Jonathan Smith. He and his colleague, Lawrence Thornbury, a former professional actor and also a wonderful drama teacher, were casting Macbeth. I think they intended one of the seniors to play the lead, whereas I was just 14.
They thought I had turned up to audition for a cameo role - Fleance, the son of Banquo or maybe Lady Macduff's son. They were taken aback that, actually, I was interested in playing Macbeth himself. But they must have seen something in me. I ended up with the role.
In the oddness of the public school system, English and drama were my salvation. Jonathan and Lawence made the English department feel like a special place; they also recognised my passion for acting and were able to channel the various problems I might be going through as a teenage boy on to the stage. It helped a lot.
I ended up acting in many school plays, but the ones I remember most were those directed by them. These included Murder in the Cathedral and Henry IV, Part I. It feels as though I basically cut my acting teeth with Jonathan and Lawrence.
My relationship with Jonathan runs deep. He was a great mentor and always had a wise word to say about something, but never in a patronising, now-sit-down-and-listen-to-me-sonny kind of way.
I can remember, for example, the day when, in not so many words, he suggested that I might enjoy Cambridge. "Trust me," he said, "You'd fit right in." If he had cornered me and barked, "Stevens! Oxford! Magdalene College!" I'd have thought, 'Oh sod off!' But it was just a subtle intimation and when I went to Cambridge to see it for myself I thought, "Umm, the old boy might have been on to something here." I ended up loving Cambridge, studying English and getting involved with the Footlights dramatic club, which was perfect for me.
I have never lost touch with Jonathan. He comes to see me whenever I am on stage and in recent years, too, we have worked together on several occasions. He gave up his job as head of English at Tonbridge to pursue his career as a writer. Just recently, I did a Radio 4 play that he wrote, and we're trying to adapt one of his six novels - Summer In February, which is about the painter Alfred Munnings.
Jonathan has also written a couple of memoirs. The first, The Learning Game, is a beautiful book about his philosophy of teaching and how to extract the best from young minds: a subject he knows so much about. The second, The Following Game, is about watching his son, Ed Smith, grow up to be a professional cricketer who played for Kent, Middlesex and England. Very flatteringly, in the latter he also included a little chapter about me and about the writer Vikram Seth, who was another of his pupils.
Jonathan is just as good at writing as he was at teaching. And that, believe me, is saying a very great deal.
Dan Stevens plays Matthew Crawley in the new series of 'Downton Abbey' from 18 September on ITV 1.