My DS is 25 now (so the following might be a bit out of date!) but his Grammar 6th Form told students to pick 4 A Levels but they were only really expected to sit for 3 by the end of year 13.
This was so that if (when?) a pupil realised they had made a grave mistake and couldn’t possibly continue on with the now-despised subject, they would still have 3 A levels worth of UCAS points and be able to move up to uni with their classmates (and not have to spend another year cramming in a third A Level at a FE college).
This worked particularly well back when you could quit a subject at the end of Year 12 and still end up with an AS level. Under that system the 4th subject didn’t feel like a waste of time because you still had something to show for it.
By the time DS was in 6th Form most subjects had done away with the AS Level and the others were phasing it out.
Not sure exactly why the Government ditched it but my son’s teacher said exams at the end of each of the two years had led to more time revising the subject matter than actually learning the subject matter, which is clearly untenable. Returning to just A Levels allowed for a better learning trajectory, yet it seems to me that 4 subjects is almost a relic of the AS level times? As in, it was normal to study 4 subjects at the beginning of Year 12 but it was with the aim of finishing Year 13 with 3 A levels and 1 AS Level.
That said, it’s clear some teens are more than capable of taking 4 subjects at A Level and I wouldn’t want that opportunity to be removed from them just because it’s not necessary for University applications.
I suppose the challenge is how to cater for a wide range of learning styles and personality types?
Because the safety valve of a droppable 4th subject is crucial for some teens but at the same time, 4 can be an awful lot of pressure on the diligent, perfectionist teens who wouldn’t consider any subject droppable under any circumstances - it’s great to aim high academically but not if it’s at the expense of mental wellbeing or leaves no time for creative extracurriculars or hanging out with peers.