Mr C of ??? my old Junior school in N London was a dab hand with the ruler, applying it to both boys and girls on the back of their legs.
Miss B of the same school once rulered a girls palms until the ruler broke.
First years on their first day at my secondary school had to endure a machine gunning from the headmasters old army BREN gun, those that were killed had detention for the rest of the week and the wounded were merely caned by the butch gym mistress.
A thick heavy plastic ruler to the hand or calf, probably not used in your country but used in others really stings for a second or two. Enough to wipe away any smile. The big loud slap it makes has a good dramatic effect on the rest of the class.