You were fortunate! In our girls grammar school we had to keep to our uniform, VIth form or not!
As you can see no uniform meant, longs, no ties, and more importantly no caps.
Did you still have to wear hats, different ones for summer and winter, and knell to show that your skirt was not too short? My wife did.
We still had to wear shoes with 'rubber or part rubber heels' for safety on the stone stairs, didn't understand that and still don't.
Part rubber was a segment of rubber at the back of a leather heel, useful really because this could be cheaply replaced without the need for a whole heel