My friends struggle to understand why I choose to spend my life in a classroom trying to instil a love of literature in teenagers. Sometimes it is easy to see their point.

We may find great satisfaction in our rapport with students or through presenting our subject in a variety of creative ways, but rarely can we look back at the end of the day, pinpoint something specific and say, “Look at what I achieved.” I sometimes lie awake after a day’s teaching and an evening’s marking, wondering what on earth I have to show for all my hard work.

Recently, however, a couple of chance encounters with past pupils have meant that I have been able to drop off to sleep immediately, with no need to search my heart in order to justify my existence.

Two weeks ago on a train, I was immersed in my newspaper when a young woman leaned across the aisle and asked if I worked at the local college. I immediately remembered her as an A-level student I had taught about eight years ago. I had dim memories of having averted a crisis by convincing her that halfway through the course was not a good time to pack it all in and go travelling with her boyfriend. A bright girl, she had gone on to achieve three good A-levels, then gone travelling (with a different boyfriend) and now had a good job.

“I wouldn’t be where I am now if it wasn’t for you,” she said.

And then, out of the blue, another past student emailed, inviting me to meet for coffee. Intrigued - because my memories of him were of his furious face and dark comments as I told him to put his phone away for the 20th time in as many minutes - I accepted the invitation.

Over coffee, he told me how much he had learned from me. Apparently, in spite of fighting me all the way, he had actually loved my lessons because I had fought back and made him work. He now hopes to become a teacher himself.

The job may not yield instant, visible evidence of our hard work. But when we do catch a glimpse of the part we have played in enabling our students to achieve happiness and success - well, it makes the job more than worth it.

The writer works in further education in the North of England

Tell us what keeps you awake at night

Email jon.severs@tes.co.uk