Through an amalgam of humour, challenge and interest you just know that you have taken your students somewhere. This doesn't happen every day - we all know that - but those diamond teaching moments fill you with a sense of purpose and worth. Why then did I say to myself at the age of 49, "enough is enough, it's time to quit"?
It wasn't a snap decision. Life-changing decisions rarely are. But it's usually a single event that focuses you: suddenly you know what you have to do.
I'm not sure what precipitated that process in me, but it may have been the day a colleague came into one of my Year 9 English classes. It was a great lesson. There was discussion, humour, a range of activities, all the kids involved - it was one of those "diamonds".
My observer had a task: to fill out a ticklist. After the kids left, she presented her feedback. It was all about the boxes that hadn't been ticked.
Although I was considerably deflated, I don't blame her. She was doing what senior management wanted her to do and she was focused on her task.
While I was teaching the only way I've ever been able to, straining to make every lesson the best I could, often working from instinct and intuition, those in charge were checking to see if all the Ts were being crossed.
It suddenly dawned on me what an enormous amount of mental and emotional energy I was putting into my work; energy that could possibly be channelled elsewhere. In several schools and despite glowing appraisals, I'd endured more and more people coming into my classes with clipboards. I'd jumped through all of the hoops like a trained circus dog.
Would there ever be a time when they'd say I was doing it right? Would they ever leave me to get on with it? Could I ever fight my way through the burgeoning list of targets, focuses and assessment objectives dictated by Lilliputian administrators? I realised that they didn't want people like me any more, great exam results or not. I was never going to be able to do it their way. I was a cavalier peg in a roundhead hole.
My decision made beautiful sense. I would leave teaching, never to return, no matter what. No supply teaching, no nothing. So I did.
Do I miss it? Yes, especially those magic experiences with the kids. But I don't miss the institution. Despite a successful 20-year career in the classroom, I can honestly say that I don't think I've ever really liked schools.
Doug Jenner lives in Hertfordshire. He is now a full-time writer