The school was undertaking some short, unannounced observations. The scary and humourless deputy head would come to a lesson, check out learning objectives, books and lesson plan and watch for a few minutes before leaving.
I had been late at a parents' evening the day before and was thoroughly unprepared. You name it, I hadn't done it. If anyone dropped in, I was for the chop.
We were warming up with a quick-fire French question and answer session when he walked in and sat down at the back. "Bonjour" I said nervously.
"Bonjour", he replied, "Ca va?" My heart sank, he was toying with me.
I paired him up with one of the pupils and they started chatting away in broken French. He seemed to be enjoying himself and so, as I handed out some listening comprehension answer sheets, I took a deep breath and placed one in front of him.
He wrote his name on it. We played the tape, peer-marked it and he got a B grade. I gave out writing frames and they started writing about their holidays.
Walking round the class, I saw that he had been to "Sardegnia" so I bravely pointed out his mistake and gave him a bilingual dictionary. "Merci," he said and returned, studiously, to his work.
Having dismissed the class I waited for the telling-off that I knew was coming. "Wonderful, brilliant lesson," he said, "I had a marvellous time, excellent resources, keep it up. Au revoir."
I had just started at a nice rural middle class school after six years in a tough urban comprehensive and had been lulled into a false sense of security.
It was my first cover lesson and, as I walked into the classroom, I saw a boy in the far corner grab a classmate's head and smash it, nose first, into a desk.
The victim sat up, holding his hand to his face, thick, dark blood oozing between his fingers. For a moment I froze; panic started to set in.
Then my brain slotted back into experienced teacher mode and I knew what the priority was - get over there and stop him being damaged any more.
"Stop doing that, now" I boomed as authoritatively as I could and marched across the room with 25 pairs of eyes following every step.
By now, the boy with the obviously broken nose was rocking backwards and forwards on his chair, moaning pitifully, bent double, clutching his face.
My pulse must have been close to 200 but the mantra in my head was chanting: "Keep calm, keep calm."
I stopped in the corner of the room, glared daggers at the aggressor and was just about to kneel down beside the bloody child when he sat up straight, smiled at me through reddened teeth and opened his hand to reveal a theatrical blood capsule.
The class erupted into cheers and applause as the voice in my brain changed its chant: "Don't kill him, don't kill him."
Dan Tweed is a teacher in Sussex