You have to appreciate mate, that if you are awarded a sponsorship scheme, the provider has to be sure that you have all the right attributes and a reasonable chance of coping with the amount of work you are expected to do.
As well as your personality, you must reach a certain standard with your ability to learn. Of course, having a reasonable education from school will show this and initally get your foot in the door, i.e. your application will be accepted. Also, and I don't know this as fact, but I am sure it is used as a filtering system too.
If it is any consilation, I didnt do particularly well at school, however, when I got to college I extracted my thumb from my butt and did some work, to which I got the results I wanted. I think I applied to BA about 4 times, and every time they rejected my application until I got a degree. Then I failed the verbal reasoning test after been invited for phase 2, aptitude testing
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With the above in mind, you also have to realise that sponsorship is very competitive, and only a few people get through. I lost count of how many times I was rejected, but if you are determined enough you will get there, even if that does mean saving for a few years to fund yourself.
All the best with it.