My classes expect soccer and rugby on Thursday, not an hour of drama. The cast expect an audience of Mums and Dads. Heckling from Year 11 yobs could wreck their confidence.
Tuesday: Stuart, the Sadistic Dentist, is needed for a careers interview after break. He isn't in the music room running through his songs, or in CDT helping to paint the big plant.
Involving Stuart in the play is a desperate attempt to improve his attendance. At break I drive round to his house. I bang on the door and bellow through the letter box for 10 minutes.
"I thought you were social services," Stuart explains, tumbling into the car. "I was learning my lines." I beg him not to tell his year tutor this until after the big night.
Wednesday: The voice teacher complains of sexual harassment. At break the chorus girls surrounded him at the piano and pressed their young bodies against him. "They admire you as an artist," I suggest. He isn't fooled. They ambush him again at lunch time, force-feeding him chips in curry sauce.
Which of them is destined for stardom? He is naive. He tells Nadine Logan she has perfect pitch. Her rivals turn on her. He has to be rescued from the fight by a dinner lady.
Thursday: Full dress rehearsal. The Sadistic Dentist makes it to registration for the first time in months. The chorus girls charm my Year 11 football hooligans into singing along and even hand-jiving.
The head pops in to see how things are going. "Has it helped, rehearsing with an audience?" Our hero, the Eccentric Horticuluralist, is close to tears. "I can't sing," he sobs. I already know. He can't rap either. We've tried everything. Mark is tone deaf, but he does get more laughs than the rest put together.
"Mark, your atonality is part of your comic genius," I say.
Friday: Testing out curtains, lights and radio mikes. Some of our singers don't have the "oomph" for a large theatre, and can't make themselves heard above our hyperactive drummer. The mikes give them confidence and make them feel like professionals. As the audience settle into their seats I still feel uneasy. Maybe this sort of thing should be left to experts.
Switch on the chorus girls' radio mikes just before curtain up. "FIVE, SIX, SEVEN, EIGHT . . ." booms from the speakers. I dash to the sports hall and beg the step-aerobics instructor to switch his mike to another radio frequency.
The Mums and Dads love it. The chorus girls kiss everyone. The staff move on to the pub, to relax and unwind. The kids have beaten us to it.
The chorus girls overwhelm the helpless voice teacher. How will I explain whatever happens next to an outraged headteacher on Monday?
Ian Campbell teaches at The Leys High School, Redditch, Worcestershire.