Well my initial response is 10% of what kind of cohort? His position in his year group is irrelevant really. What kind of national curriculum levels are you talking about?
But, yes, of course he can exceed expectations of him at this point. Hard work and determination will be one thing - the main thing.
Focussing on key subjects when it gets to options will be another.
Making sure he has all the support he is entitled to in class and out (looking at strategies to improve his areas of weakness; can he word process better than write? can he have notes copied for him? can he sit nearer the front? or whatever helps).
Maybe try a training programme for working memory issues (see recent thread)?
Is behaviour/attitude an issue? Work out some appropriate rewards for improvement.
Does he have an idea at all of what he would like to do later on? Focussing on a goal can make lots of people improve their attainment through sheer determination as well as interest and passion.
Make sure school know you are a committed and interested parent and they will meet you halfway (I'm sure you already have!)
Really, I think knowing where he's headed is the most important thing. Say, he doesn't get brilliant GCSEs but still goes down an academic path onto A levels - some students do do lots better at just four subjects than ten. Or if he chooses another path, he could be much more successful in the mature environment of college, work or apprenticeship.
Nothing is set in stone, I absolutely believe that (and really have to cling onto that hope for my own ds, honestly - bright as a button and doing very well academically but with his autism he has his own difficulties of socialising and meeting expectations of behaviour that I have to believe will improve slowly!)