Booby trapped chalk
Circa 1991. It was one of our teachers* that told us of a prank where you drill a small hole down the centre of a piece of chalk, insert a non-safety match and seal the hole with chalk dust.

Sounded like fun, so we did.

Usually there would only be a few small stubs of chalk near a blackboard so when the Further Maths teacher sees a nice, new, full-length stick of chalk in the middle of his desk he really should have suspected something.

Class proceeds and those pupils in on the joke paid incredibly close attention to every mark made on the blackboard until eventually the chalk wears down, match head is exposed, strikes, and flames erupt from the end of the chalk.

Cool as ice Further Maths teacher, pauses and looks at the flaming end of the chalk.

"Oh, very good, boys" he says, turns the chalk stick around and carries on.

Emboldened by our success we repeat this with the nicest gentlest teacher there ever was. Applied Maths.
When his chalk stick splutters into flame he is visible shocked and confused, drops the flaming chalk like its on fire (it was)

Turning to the class, "I hope none of you boys were involved with this" he said obviously very disappointed. We felt so bad we owned up immediately.

*Moral of the story - pick your targets wisely.
(Rich T has a clever and witty sig, Sat 10 Sep 2011, 17:01, 3 replies)

I wish I'd known about that one.

( moonbadger Doesn't judge a fish by its ability to climb trees, Sat 10 Sep 2011, 21:20, closed)

*this is a footnote

( monster munch person, man, woman... camera... TV?, Mon 12 Sep 2011, 10:23, closed)

footnote corrected - ta!
(Rich T has a clever and witty sig, Tue 13 Sep 2011, 12:58, closed)