Which fourth A-level is better alongside Physics, Maths and Further Maths? Or are chemistry/economics equally good choices?

Check with the school / college, but if he's as bright and good at maths as you say and can read up a bit over the summer, I would think he could do just fine without the GCSE.

I would leave the economics as the thing to think about after school (and possibly / probably drop). It's not studied technically in school, which may frustrate him, and means that university studies have to start again anyway. But the interesting relevant bits are easy to follow informally via pop econ books and blogs: start with Tim Harford, and also look at https://www.core-econ.org/ if he really wants to spend time with it in his evenings. Actually, even if he were to completely change his mind and want to do economics at university, computer programming would be a better A level preparation than economics A level.

Chemistry: nothing against it but it sounds like it doesn't excite him and it wouldn't develop useful skills or a wider view of the world in the same way as computer science or economics would.

I think it is fine to have not done the GCSE - here’s info from Farnborough Sixth form college, one of the large well rated colleges in our area:

Q: How much overlap is there between the GCSE and the A level and is it a problem if I've not done the GCSE?
A: They overlap a lot, and if you've done a Computer Science GCSE (particularly with the OCR exam board), you'll find the first half term quite familiar. However, a good number of our students take the A level without a GCSE and they perform well. The most important things are that you have good logical thinking, some numeracy skills, an interest in the subject (see course content above) and tenacity. You can't give up each time your code gives an error.

I would always recommend geology / geophysics, it’s a wonderful cross disciple science as well, but sadly very few places do geology / geophysics a levels. A few do, but even the enormous 2000+ student sixth form colleges we looked at didn’t have any geo a levels. Most of the geologists on my undergrad were taking it up for the first time.

Same for us. If he’s y10 there should be time for a few open day visits - they often run them around now, and again in the autumn and my sons both found it v helpful going to as many as possible (eg visiting same college a couple of times) to talk with the subject teachers and find out a lot more about the courses. They often run taster days too.

FWIW I knew a few very hardcore physicists at Cambridge who ended up branching out into more multidisciplinary physics/chemistry/applied maths linked areas, at PhD level anyway. At school the subjects are so restricted compared to at uni, of course. I found that quite a lot of chemistry at uni turned into maths, so he may start liking it more the more he does!

Does his school offer proper computer programming as an A level (NOT IT)? He's likely to need to code in a scientific career. Lots of people pick it up via following examples on stack exchange etc, but having a bit of a grounding in how things properly work can be valuable, and might set him up to be skilled in something very useful throughout his studies. It's as well regarded as a science A level.

I did Maths, FM, Physics and Chemistry with the aim of either Medicine or Physics at uni.
By the end of sixth form I no longer wanted to do Physics and in fact I ended up studying Biology (Scottish uni though I think I could have done Biochemistry in England without Biology A level) and Chemistry was compulsory in the equivalent of English first year. I would bear in mind that he may change his mind about his degree and that Chemistry will help with Physics.
However I really didn't like it at A level and I was annoyed to have to do it at uni! I really enjoyed Biochemistry - the chemistry was just different - and I enjoyed physical chemistry because I still loved physics even though it wasn't my uni subject.

For those saying why do 4, it was a few years ago when I did my A Levels, but doing 3 was still typical - I did 5 AS Levels and 4 A Levels + General Studies. And one of those was a GCSE and A Level in a new language in two years.

I managed learning to drive, a part time job and an incredible social life too.

I thrive when I am so busy that every minute has to be accounted for (and now work in a high pressure job because I do not perform at all where there is plenty of time and no deadlines), so for some students filling up with more A Levels is the right answer (I got 4As and a B in the day before AStars).

But would they have missed their grade requirements if they had focused on 3 A levels? We’ll never know but having 25% less work surely would have made a difference!

ds has studied maths, further maths physics and Welsh bacc. Welsh bacc was all done by February half term in year 13 so no distraction at all from A level revision. That seems a good compromise.

Both are good so he should do whichever he enjoys most.

In my role I look at a lot of CVs and on balance I’d have a slight bias towards economics as it shows an interest / engagement with the human world (terrible choice of words - hope you understand my meaning). It’s a good compliment to maths but also has elements of history and politics overlap.

Another factor that could help him choose is which A level teacher he’ll like more.

If he has to do four he guided by what we're his top GCSEs and which was his favourite subject. He'll never go wrong.

I had in mind the areas you flagged @ErrolTheDragon and better articulated than I would have done!

I did those plus economics. In my field (finance) the economics is so useful.

chemistry

@Baddogs it was mainly to address the better to get 3 A stars than 4 As type conversation from others not really aimed at your son. It does all depend on the child. As your son is only in year 10 then he has time to look into the A level subjects he might take. There are a lot of students who posted on Youtube about chemistry and other subjects at A level, might be worth looking into.

Mine found 4 A levels relatively easy as did their friends, all of whom went onto RG or other high ranking unis. Both mine needed maths/fm for their subjects at uni and they are very maths brained.

Re the workload of 4 A levels - if they’re aiming for a top STEM uni then they’ll need to be developing their time management and study skills anyway. It really doesn’t sound like it will be a problem for your DS, OP.

I’d be interested to know what @PerpetualOptimistwas thinking of too, but for sure there is a lot of exciting interdisciplinary work at the moment in the area of new materials (eg ‘high temperature’ superconductors, battery technology…) and also in the very broad area of biophysics and ‘structural biology’. That might sound like you’d want to do biology but I think a sound footing in chemistry would be more relevant.

My DD will be taking Maths, Physics, computer science and French. But she wants to study CS at uni.

Geology would help open up geophysics as a career, which can include (exo)planets, climate physics and seismology