The bite of the cane.

There were a few girls, who - never having felt the rattan across their backsides - denied that a caning could be as painful as people claimed. Emily was one of them. She scoffed at the howling that could be heard from within  the head's study as the whack of the cane across bare cheeks echoed down the corridor. "Sissies," she would mock them, as they emerged red-eyed and rubbing their bottoms, "drips, weeds, it can't hurt that much."
She herself had only been spanked twice: once with a hairbrush by the Deputy Head, and once with a slipper by her Dormitory Captain. On both occasions, although she would have denied it, she herself had yelped loudly as each smack landed.
Her under-estimation of the efficacy of rattan on bare skin led her to take chances that a more prudent girl would have avoided. Thus, when she was caught out of bounds buying sweets in the local shop, it was with some surprise and alarm that she found herself bending over the Head's desk, her knickers around her thighs, listening to the swish of approaching doom.
'I'm sure this can't be too bad,' she thought to herself as she felt the cane tapped against her bottom. 'It may sting a bit, but probably no more than the hairbrush.'
She sensed the cane being drawn back. 'If I grip tightly on to the edge of the table, I'll be able to get through this with no trouble. I'll show them.'
She heard the sighing swish of the descending rattan, the loud crack of the impact.
"OOOOUUUUUWWW!!"

(For what happens to girls who get caught out of bounds, read the Bexhill School series - see below)

TV is bad for you (or at least, your bottom)

The strict rule when Debbie was staying with Aunt Alyse was: no TV until after all the homework is done.
So when the aunt returned unexpectedly early and Debbie was perched in front of the box watching Coronation Street, it was not surprising that Aunt Alyse asked to see the completed schoolwork. Of course it wasn't 'completed'; it wasn't even even started.
This was the bit Debbie almost hated most: the moment when Aunt Alyse told her to go and fetch the hairbrush. It was an evil implement, long and stingy. It lived in the second drawer down in Aunty's wardrobe.
When she got back with it, Aunty would - as now - be sitting on a chair. She'd silently hold out her hand for the brush. Debbie knew what had to happen next: she'd have to peel down her panties, and lower herself over Aunty's  lap. Then she'd feel her skirt being folded up, the air cool against her bare backside. That was the moment Debbie would let go of her aunt's knee and put her hands on the floor or grip the legs of the chair..
All this seemed to take ages: the awful prelude to what was about to happen. Any second Aunty would start. The whacks would rain down, each cheek addressed in turn, each smack of the wood against Debbie's reddening bottom feeling like the sting of a bee. She knew that within a minute she'd be howling and kicking, but the spanking would go on and on and on.
How she wished she wasn't addicted to Coronation Street.

(The photo is probably from Nu-West/Leda. Acknowledged with thanks to this seminal site)