Back in the day when Twiggy was a model I had to wear a tunic for school. The skirt length rule was maximum of 3 inches above the knee or, when fashions change - as they did about 1971 - 3 inches below the knee. When kneeling down.
Part of the uniform was a canvas purse belt. It was against the school rules to leave any money in cloakrooms, blazer pockets etc. You put it on just below your diaphragm and then pushed it down to your waist.
Skirt was instantly about 8 inches above the knee. 800 girls of in black mini-skirts. 4 inch heels. We played lacrosse. We looked just like St Trinian's.
The school was direct grant, 20% went to Oxbridge, so it wasn't a question of low aspirations. It was the fashion but thankfully a lot less 'pornified' than today. Knickers were bikini type not thongs, thank God.
Brilliant from a financial pov - I used to make skirts from half a yard of 36-inch wide material, a deep hem and a waistband. About 16 inches in length.
My DM didn't mind, either I was eligible for free school meals so saving money was important.
As many have said, we were expected to judge what was appropriate and stick to it.
Some rebels took great delight once we got to LVth and could wear skirts to delay going into summer uniform and just stop wearing jumper but with a coloured bra so fluorescent that it could be seen from outer space.
Up until about 1969 most bras were white. The Wonderbra only came on the scene in about 1974-5 from memory.
I'm getting old