But the other day I was presented with a profound moral question which has since kept me awake. The cover work was an unashamed hour-waster: "write five things which are good, five which are evil - give reasons".
No problem there, I thought, set the work, grabbed my su doku and settled in for a peaceful hour.
As I laboured, I could hear the comforting consensus of mumblings from the class. Chocolate: good. Homework: evil. Alton Towers: good. Dinner lady with wooden leg: evil. No surprises. Then, a dissenting voice. "Sir, I can't think of anything."
With a heavy heart, I laid my puzzle down. "Come on, 'good', you know: fluffy bunnies, Christmas, Gandhi, gravy, free stationery, Britney, tax rebates, ice cream. Evil: war, disease, housework, Blair, walnut whips, child abusers, cover lessons, it's easy."
He thought. In a film with Macaulay Culkin, smoke would have plumed from his ears - then the light bulb.
"Got it Sir! Bill Oddie, Sir."
"Bill Oddie, Sir. He's evil."
I tried to reason with him. "Really? The bloke off the telly? With the beard?"
"Yes, Sir. Him. Evil, Sir."
I sniffed the air for the tell-tale smell of marijuana. Nothing. No empty beer cans lying about, either.
I joked. No, he's not evil. He's one of the Goodies! My retro joke lost on this 12-year-old who probably thinks Vicky Pollard is comedy history now Catherine Tate has come along.
"No, Sir. Not a Goodie. One of the baddies."
Did he hate birdwatching? Or just men in Barbour jackets lurking in bushes with binoculars?
The boy went back to his list, but I was troubled. Could the genial ex-Goodie TV-presenting birdwatcher be a bad 'un? Perhaps his family and Oddie's had been locked in a blood feud for generations. Or was it the beard?
Intrigued, I inspected the class's work. When I reached the Oddie-hater I peered over his shoulder and saw the words neatly inscribed in the evil column: bin Laden (say it fast in a noisy classroom, with a CockneyBengali accent to a hungover teacher, see?) So, Oddie isn't evil. But it still made me think how evil isn't as absolute as we expect. I was prepared to think that the hapless Bill - one of the nicest blokes on TV by all accounts - was as bad as Osama. True, no major acts of terrorism to speak of. But a simple cover lesson had made me think how communication - or the lack of it - can affect our view of the world entirely.
Just to be safe, the next day I shaved my beard off.
Julian Kaufman teaches in a secondary school in east London