Without wishing to deviate the thread (which has been really helpful), I did just want to follow-up on a couple of points which focus more on careers (which have been kindly offered, given I mentioned IB)
@trubbelatmill if you were aiming to say that graduating students can't just walk into a career, I would say that that was also the case for the majority in my day. The graduate job market at the moment is a challenging, but it was still hugely competitive when I did my degree. I do agree with you that there are even more graduates, but I think there have always been a tiny minority of careers people could just walk into (there were some that were possibly open to people with a huge level of privilege, and those are perhaps even smaller - which is why there are comments on Mumsnet about 'not even with an Oxbridge degree...').
I did mention Investment Banking in this thread, because that is impacting what universities my DD is aiming at. However, in line with what you are saying (although possibly with a different take on it?), I do not think that someone in Y12 can or should assume they can determine their career path now. There are too many uncertainties. My guidance for my children, at every stage, is to try to focus on what their passions are at that moment, and to pursue the things that they enjoy/are interested in/are good at. At each point, they can (and should) interrogate what is working for them and the things that aren't. It might not mean things are totally right, but it is less likely things will be totally wrong.
For that reason, I am supporting her choice for IB feeder universities (although I would prefer if she would consider less competitive universities too). If she doesn't decide to pursue IB, those universities will still be fantastic universities. But the most important thing for me is that she choses a course that she thinks she will enjoy. Because that is most likely to lead her towards a career she enjoys.
I know two people who 'chose' their career, based on what they studied at university as a teenager - a lawyer and a doctor. Even within my career (I'm an academic) the majority of my colleagues did not chose their career that way. I am a firm believer that the only way to find joy from your work is by following the subjects or ways of thinking/doing that interest you. I think that there is a tiny (miniscule?) number of people who decide what they want to do as teenagers, and actually are able to enjoy that career for their whole lives. I believe, more than ever, not only do jobs change, but careers change. I think that flexibility is going to be even more crucial as we move further into the digital age.
@Ceramiq Your experience on IB is helpful, but I think my approach to advising my DD is likely to sit in contrast with the approach you would take, but I think we will need to agree to disagree. I have advised my DD that courses in Computer Science/Maths/Economics would be useful. But she doesn't want to do any of them as a single subject. I am not going to tell her that that absolutely rules out IB for a career, because it may not (she recently met a (relatively) young woman at an IB internship who was a History graduate), and because I think that what is most crucial is that she does something she will hopefully love at University., Whatever the state of the job market, for the vast majority of children, I personally do not think you can (or should) try to determine their career at 16/17 because they just don't have enough experience of themselves or life to know. The exception is the minority of children who are clear themselves about what they think they want to do (and their choice sits in line with their capabilities, and they aren't just trying to please parents by doing law/medicine etc).