One’s actions in the opening moments of meeting a new class will set the tone for the rest of the lesson, possibly even for the entire future relationship with a group of students.

The beginning of the lesson is even more crucial for the supply teacher, who, from a standing start, must mark their territory, own the space and set the boundaries – all without coming across as too much of a despot. It’s a tricky balance to strike. As a teacher of some 20 years and now a year into doing supply work, I was confident I had these basic moves locked down.

It was a science lesson. It was Year 9. It was the last period of the day (astute readers may be able to spot where this is heading). The lab was in a remote part of the school and my supply teacher senses quickly recognised this meant it was far away from the attentions of any senior staff wandering the corridors looking to pull the kids into line. Judging by the behavioural entropy of the class waiting for me, the kids sensed this, too.

I managed to get the lab unlocked by nabbing a passing teacher, who then kindly went in search of some cover work while I stayed with the class. The kids meanwhile, had seen the open door and began trying to get into the room. I stayed where I was, blocking the doorway.

“Sir, are you taking us for science?” a small scruffy-looking boy asked. I thought I could detect a hint of glee in his eyes.

“Yes,” I replied. Keeping the banter to a minimum at this stage is usually the best approach.

“Where’s Mr Crabtree?” a gawky girl, towering over the small scruffy boy, asked.

I’m asked this question at least twice every day; every time I fight the urge to say: “He’s dead.”

“He’s not here today,” I answered.

“Sir, can we go inside?” they both asked in unison.

Now I had a crucial decision to make. Did I let them into the room, not knowing how long it might be before I had any work to give them? Or did I keep them outside and try to get them to line up?

Supply teaching: Show no fear

Normally I’d go with the first option, as forcing them to line up can feel like trying to assert excessive control and might well give the chippy students an opportunity to start protesting. Besides, it gives everyone something to be getting on with.

This time, however, I decided to keep them outside. I could see they were a lively bunch and I didn’t much like the prospect of having to turn my back on them for two minutes while I wrote the work up on the board. A lot of unfortunate things can happen in two minutes with your back to a class. Surviving in the capricious world of supply teaching demands the ability to think ahead and anticipate trouble before it strikes; it’s like a game of three-dimensional chess with whiteboard markers.

There was still considerable "enthusiasm" from the students waiting in the corridor, and so I asked them to line up in an orderly fashion, which, to be fair, a few of them did. Most did not.

I tried again and a few more shuffled reluctantly over to join the others. I raised my voice a decibel or two, adopted the assertive-yet-non-confrontational body posture that said I now meant business, and fixed those students still arsing about with a steely gaze. Nothing.

A few of the students who’d already lined up abandoned the line and went back to join the ones still charging up and down the corridor. In situations like these, you have to hold your nerve. It can seem like an eternity standing there in silence, waiting for everyone to bend to your will. So I waited. I waited, and they ran around putting each other in headlocks and throwing water bottles. Still I waited. One by on,e I picked them off with a penetrating stare that said, "Stop being a dick and line up!" and ever so slowly the wrestling became scuffling and then shuffling until finally there was a ragged line and an uneasy calm. My dogged patience and years of experience had triumphed.

And then a kid right at the back of the line realised that the other door to the lab was unlocked and disappeared through it into the room, swiftly followed by everyone else.

Now I was alone outside the lab while they were all inside re-enacting the Mongol hordes’ invasion of Europe. Not for the first time I’d been outwitted by a bunch of 14-year-olds. Oh well, it’s like they say: every day’s a school day.

The writer has recently taken up supply teaching after 20 years in a full-time teaching job