The best schools organise careers fairs. My DH talks about Civil, Structural and Environmental Engineering at his old school and others. He often has quite a queue at his stand and can advise on the most appropriate courses and further training required to get Chartered Enguneer status. Both the schools our DDs attended did the same and lots of parents came in from Accountants, Solicitors, Hospitality, Vets, Doctors, Journalists, TV Exectives, Artists, Engineers and quite a few others. Teachers have limited knowledge but I have found the online newspapers have quite good information, eg The Independent.
I do not know how schools can advise a student on A level choices if the student has no idea what they might want to do and the school has never raised the issue with the student. There are plenty of cases where failing to do Maths, for example, will end up being a problem. There are plenty of students though, that know they are good at a few subjects and will enjoy doing one of those at university so put off making a career choice until they are older. Many, many students did this years ago and no-one thought the worse of them for it. Science and Economics students seem to know earlier than the Arts people.
When I was at school, in the 1970s the careers advice at my Grammar School was non existent. We just found out for ourselves. That is something we should encourage. Self reliance and finding out for yourself. This sorts out the movers and shakers in my view. I do agree with better careers advice but it should be a partnership between school, parents and students to do the research.