I guess I feel that there should be motivation for children to achieve or else you will get the feeling of 'what was the point of all those a stars when I didn't really need them for the course I am studying'?
I understand what you're saying @mids2019, and to some extent, I agree. However, I think this is partly for parents to manage, primarily through the values that they pass on through their children.
I have always taught my dd to do her best, because there is a real sense of achievement and satisfaction in doing as well as you possibly can in any endeavour. It is what my parents taught me, and I have tried to pass it on.
So in our house, the purpose of those A*s or grade 9s is not to get into a specific university or land a specific job or whatever. The purpose was simply to do the best that you could do because taking pride in your work is inherently more satisfying than doing a half-arsed, mediocre job. If it turns out that your very best effort was only a grade 6, then no worries, as long as you have genuinely given it your best effort.
In my view, if you look at hard work as a means to an end, you will inevitably be disappointed sometimes. Kids who work hard and get perfect grades won't all get into Oxbridge. Adults who work hard won't always be rewarded with the promotion that they deserved. People who make every effort to look after their health still get sick. Life is like that, and it isn't fair to give kids the idea that they can control the world or guarantee their success through their own effort - they can't. I have taught my dd that hard work, effort and persistence are always a necessary conditions of success,, but they are not sufficient - there will always be an element of luck involved as well. If things don't work out as you hope, at least you'll know that you gave it your best shot.
I think the other issue that can be problematic if you focus on the "means to an end" approach is that, even if you are lucky enough to succeed, people can sometimes get very disillusioned when that the much desired end for which they worked so hard turns out to be not quite all that it was cracked up to be. I knew quite a few students at Cambridge who were faced with a bit of an "is this it?" moment during their first year. They had spent so much of their lives prior to university aspiring to that goal, only to find that they weren't actually enjoying it when they got there. By contrast, I hadn't given much thought to Cambridge before it came to filling in my ucas form (or whatever it was in those days!) and had so few expectations that I couldn't really be disappointed.
So I don't ever tell my dd that she should work hard in order to achieve xyz. She should just work hard in order to have the satisfaction that she has done herself justice and performed to the best of her potential. The efforts that you put in are what matter to us, and not the outcomes that come out.