I was a duffer in Z, but still took 8 O levels. It was very academic, which wasn't for everyone.
Interestingly, whilst on holiday in France, a couple of years ago, a coach load of Russian youngsters arrived. They were all ballet trained. They offered to put on a show for a discount for three...
We had options at 14, so I dropped Physics & Chemistry, just taking the obligatory science via Biology. Everyone had to take a modern lanaguage, but as I was so good at French, I dropped Latin and took German instead.
It wasn't commonplace but it did happen. I wax at HCGS, from 59-64. We had three classes per year, X,Y & Z. It was mainly the X class stayed to go onto sixth form. Most of us left at16, which was a year longer than at secondary moderns. In those days 5 O levels got you into a decent job...
It wasn't so cut & dried even when the 11+ was the deciding factor. I passed and went to Hove County, but there were children who moved up at 13 because they showed academic promise, when at the secondary modern.
In those days the secondary modern didn't offer any exams at all, which was why...