Mr. Henderson stood at the front, tapping a wooden ruler against his palm to quiet the low hum. He's a middle-aged man with a receding hairline and a tweed jacket with suede elbow patches, the kind of teacher who's been doing this long enough to have perfected the "I'm not angry, just disappointed" stare.

The door is still closed. The only sound is the fluorescent hum of the lights and the shuffle of a dozen students repositioning to get a better look.