Whoever gets to play the xylophone,” says Mrs B, to her class, “will need to be - JIMMY, IF YOU DON’T STOP HITTING JOSH WITH YOUR RECORDER, I’M GOING TO GET VERY CROSS - sitting beautifully in complete silence,” she concludes, seamlessly dropping back to her original decibel level. I am stunned. How did she do that thing with her voice? I am just about to take to the parquet as a first-time class music teacher and I am, frankly, terrified. With only a small, yellow tambourine standing between me and class anarchy (shake it softly and the children are surprised into silence, or so the theory goes) I’m not convinced I have the technical skills to cope.

The despised job I’ve recently left in the cut-throat world of business begins to look increasingly appealing. While middle managers had no compunction about telling you exactly what they thought of you, they could normally be appeased with cracking PowerPoint graphics and an unlimited supply of hot coffee and Danish pastries. And if they did start pinching each other under the table, at least they didn’t put up their hands and expect me to sort it out for them.

I practise my teacher-to-pupil voice in front of the mirror. Out comes something perfectly serviceable; after all, I’ve had this voice for years and it has done me proud. But on my first day at school, it becomes clear that it isn’t up to the job. Wobbling between frightened mouse squeak and virago at breaking point, it is about as effective at keeping the children in order as a can of sardines - but not as nutritious.

When I ask other teachers how they got That Voice, they look at me blankly, then all suggest the same things: no shouting, relaxed but authoritative body language. I try, but still end up hoarse, rattling that tambourine so much my colleagues must think I’ve turned into a Christian revivalist.

Then the miracle happens. I wake up one morning and find that some divine vocal agency has touched me with a magic larynx and blessed me with “TeacherVoice”, the miracle educational aid that has transformed my life. I discover its presence during my first lesson, when several of the boys are passing the time by spinning round on the spot. I ask them to stop. They don’t. I take a deep breath. “STOP THAT NOW,” says a voice. It is low, clear and impossible to resist. The children jump. So do I. Then I realise it was me.

I love TeacherVoice. With a bit of practice in a soundproof room (it needs cautious handling), I’ve explored the extent of its powers. There are four settings: warning; determined; forceful and battle-strength, which is rarely necessary. And the wonderful thing is that it works not only on pupils but also on dogs, other people’s children and, at top setting, can stop complete strangers in their tracks. It’s so easy to use. Just open the larynx and let rip.

There are social benefits, too. I have dispersed several small groups of troublesome-looking youths with a brief, “Excuse ME,” accompanied by TeacherLook (this one is harder than TeacherVoice as it only works if eye contact has already been established). And it’s not just for the serious things in life. I’ve had a lot of fun in crowded shopping arcades. For maximum amusement, I simply say “Stop that, RIGHT NOW,” and then have fun counting the guilty expressions.

There’s one disadvantage, though. Try as I might, my own children remain immune. But, hey, there’s always that old yellow tambourine. Wired up to an amplifier with the threat of unlimited repetitions of “Go, tell it to the mountains,” I find I can usually get my own way. In the end.

Charlotte Phillips once worked in sales and publicity but is now in her third year at Newland House school, Twickenham, Middlesex