Tony Bailey sits at the piano, chivvying his young singers. "Open your eyes! Come on! The audience is going to be full of people who don't know this. Imagine they're Year 2s. Would they be interested? They'd be picking their noses."
The singers, Year 6 and 7 pupils at Falcon middle school in Norwich who have given up their dinner time to take this good-natured abuse, start again. Several times. The energy levels pick up. The entries happen on time. Even the crouching moves have vim. So does the commentary from the piano: "You've got to believe it. That's it! Yes!"
When the national charity Music for Youth called Mr Bailey, a Year 5 teacher at Falcon, inviting him to organise the 500-strong Norfolk Schools'
Massed Choir at this year's Schools Prom, he said yes straight away. Then he put down the phone and panicked. "Normally they ask a county music service to organise the choir. This is the first time they've asked an individual. And what do I know? I only know about bass guitars."
This is not strictly true. Though he has been a professional bass guitar player - "in (orchestra) pit bands and on the QE2; not much sex and rock 'n' roll" - in his late 30s he took a music degree, realised he wanted to teach and joined Falcon middle school 22 years ago as a classroom teacher.
He started by tuning the violins in the school orchestra. Since then he has built up two choirs, "the world's only recorder marching band", handbell players, morris dancers, a community orchestra and an opera group. He is paid for three hours' music work a week, but puts in time before and after school, and most lunchtimes.
Mr Bailey also writes music for the children to perform: Gilbert and Sullivan medleys for descant, tenor, treble and bass recorders; an annual musical; and, currently uppermost in his mind, a 12-minute cantata called The Sower, based on the Biblical parable (some seed fell on stony ground, some was eaten by birds, some grew to a great height), which the Norfolk choir will perform at the Royal Albert Hall on the first night of the Schools Prom, November 7.
Two years ago, Falcon sent a video of the entire school (450 pupils in Years 4 to 8) performing The Sower as its entry to the regional section of the National Festival of Music for Youth. They received an outstanding award and performed in the national finals on London's South Bank. ("We were so big they gave us the Purcell Room as our dressing room," says Mr Bailey.) By that time Music for Youth already knew about Falcon: it had been winning awards since 1997 (the school first entered in 1994, but it takes time to grasp and reach the standards set), and the recorder band had been to the Schools Prom four times.
Having accepted last December's invitation to form a massed choir, Mr Bailey wrote to 200 Norfolk schools; 15 said they wanted to take part. He sent them the score, plus CDs of the accompaniment for those who had no music specialist (Norfolk music service has supplied and paid for staff to support schools without one), and recruited dancers and a choreographer from Chermond, a local dance school.
The teachers got together for a planning meeting in September - How many children would we need? How many coaches? How much money? - and the first joint rehearsal took place in mid-October. Mr Bailey was worried. "We had nine rows, with 60 children in each. Would I be able to get them all to stand up? Would they all start together?" But it went smoothly.
The second run-through was the dress rehearsal, bringing in the dancers and the accompanying jazz combo of conservatoire bass, keyboard and drums students.
At 10am on Monday a fleet of coaches will leave for London carrying 550 children, each with a drum made from a Pringles tube disguised with rainforest swirls. Mr Bailey will take his white dinner jacket: "MS: it's rather more cream than white these days. For me it's just a gig, so I wear the overalls." There will be a final run-through at 2pm, then the wait for their big moment: "The trio know the tempo," says Mr Bailey. "Once you've got 550 kids galloping along, you can't stop them anyway. I shall wave my hands at the right times. And we shall just go. Dum, dum, dah dum dum dum.
It'll be wonderful."