Telling them they can measure anything in the room is my first career-threatening mistake of the morning.
"Get down off the top of that bookshelf immediately...Er and with great care." My voice has risen in pitch by at least an octave. The whole of my working life is flashing before my eyes, particularly its ignominious end: "Teacher and ex-TES columnist found guilty of neglect after 7-year-old plummets to his death."
The whole class watches with unusually sustained interest as first Dick King-Smith, then Julia Donaldson and finally both the Ahlbergs fall from a great height and land spread-eagled on the carpet. Ryan alights after them and I can breathe a sigh of relief. When I'm able to speak in the lower register again, I am forced to issue a stark warning.
"No one, and I repeat no one, is allowed to measure the strip lights."
"I was measuring the secret camera that Ms Headteacher uses to watch naughty children," protests Ryan.
"I don't care what you were measuring," I snap, being careful not to reveal that Ms Headteacher's secret camera is in fact a movement detector for the alarm system. "No one is to measure anything that involves climbing on top of anything. Do I make myself clear?"
There is a general chorus of disappointment mingled with complaints that there aren't enough objects left at ground level worthy of having their lengths recorded. And this is when I make my second career- threatening mistake of the morning.
"Well then, why not measure you? Measure and compare your heights to find out who is tallest. Measure your widths to find out who is the widest. Compare the lengths of your arms and legs. See who has the longest fingers, the biggest ears and the widest grin?"
Doing practical maths is always helpful when it comes to teaching children who favour a kinaesthetic learning style. And as I have taught very few 7-year-olds who don't favour a kinaesthetic learning style, a lesson on measuring seemed a good idea.
Another compelling reason (one rarely mentioned at training events) is that it looks better to have lots of children out of their seats wandering around the room chatting to each other when they are supposed to be out of their seats wandering around the room chatting to each other than when they are supposed to be sat down answering the differentiated problems on page 27.
There is, however, a disadvantage to practical lessons, too. And it can be a pretty damaging one. The trouble with everybody being physically engaged at the same time is that it makes it difficult to spot exactly what everyone is physically engaged in. This is why it isn't until Louise complains for the third time that I, at last, begin to understand the seriousness of her grievance.
"Straighten those faces up now because I am very, very angry." The three boys try desperately to readjust their grins into something more contrite. "You must never, I repeat never, do anything like that again, do you understand?"
"I hope Ms Headteacher wasn't watching on her secret camera when the boys were measuring their willies," says Louise, after they have shuffled back to their seats.
I nod gravely. "Yes, dear, you and me both."
Steve Eddison is a key stage 2 teacher in Sheffield.