It was everyone’s nightmare: you fall asleep, dream you are in the middle of an OFSTED inspection, and wake up to find an inspector with a clipboard sitting there. That was not quite how it happened, but it was near enough.

“Could you call into school next week?” asked this primary head cheerfully. “I thought you’d got OFSTED,” I replied. “We have, so could you pop in? The staff would really appreciate it”. “Er...”

Anyway, to cut a long story short, I said I would go to this school, which I often visit, and see my friends in Reception. I love early years classes so I often take in puppets, try out ideas, tell a story, play the guitar or teach a song.

“By the way, the Reggie said he’d like to meet you. He seems a nice chap and he’d heard you come into the school regularly.”

Some of my best friends are inspectors (ah yes, but would you let your daughter marry one?), so I was happy to oblige. We fixed a date on Thursday at 2.30 for a chat in the head’s study, when Reggie was free.

I duly turned up at the appointed time, but Reggie and head were still immersed in discussion, so I told the secretary I would pop along to Reception. “Call me when he’s free and I’ll come back.”

As I walked through the door of the Reception class the teacher’s face lit up: “Oh, thank goodness you’re here. I’ve had a heavy day. Can you take them?” With that she disappeared round the corner. Gulp! Usually I prepare carefully, but this had to be spontaneous. Still, it wouldn’t be for long.

Then I had an idea. Young children usually learn about numbers representing quantities - two plus two equals four. But one of the most important uses of numbers in their lives is as “identifiers”. The world is full of them: car plates, addresses, telephone numbers. I got out my mobile phone.

“What’s this?” “It’s a phone.”

“It can’t be. It hasn’t got any wires.”

“It’s a mobile. My mum’s got a mobile.”

At this point the head walked in with Reggie, pushed him through the door, muttered “There he is”, and fled. Reggie sat down with clipboard and pen. I stood there, comprehensively sandbagge by both teacher and head. On with the lesson.

“I’m going to give you all a telephone number. You can be 1, you can be 2, you 3...”

“I want to be 3.”

“Ah, but you can’t be 3, because if two people have the same number, I wouldn’t know which one I was talking to.”

This is an important point with numbers as identifiers. They have to be unambiguous and unique - house numbers, football shirts and so on.

“I want a long number.”

“OK, you can be 123.”

“So do I.”

“Fine, you can be 456.”

Another good point. They need to know that some numbers can be long and they have to remember them accurately, or they will phone the wrong person or go to the wrong house.

I like using real or imagined telephones. It’s the same with puppets - often children who are normally silent spring to life. The use of telephone play is also excellent for children whose first language is not English. I launched into a series of conversations.

“Hello. Is that number 123?” “Hello.”

“What are you doing?” “I’m at school.”

“Good, I hope you’re working hard. Bye-bye.”

“Bye-bye, Captain.”

Cheeky, but indicative of the spirit that a phone conversation can engender. The activity offers a nice combination of number, language, and junior citizenship.

Lesson plan? On this occasion it was improvised, so adrenalin was useful, but toy or real telephones, fixed or mobile (a cupped hand to ear will do), are handy, as are stickers or cards to write numbers on, so children can phone each other, preferably sitting back-to-back for more realism.

Then think of more numbers as identifiers and categories. What numbers do you know - address, age, 999, raffle ticket, seat number? Have some examples handy.

The school received a good report, with Reception an area of strength. I like to think it was all because of my brief mobile phone lesson, but the two brilliant Reception class teachers got top grade for every lesson. Damn!

Oh, and the inspector was indeed a very nice man, just the sort of intelligent professional who humanises what would otherwise be a mechanical process.

Ted Wragg is professor of education at the University of Exeter