I hated my school days and like HH I left at 15 with no 'O' levels. 25 years later and having spent 17 of them in the RAF (non aircrew) I now fly turboprops . The difference between studying at school and studying for my ATPL's is that I wanted and indeed needed to do well with regard to the ATPL's (not to mention the money it was costing). If you can get another crack at your GCSE's all well and good if not at least try and pick up some maths & physics study packs , fortunately for you , you still have age on your side whatever you decide , my only regret is that had I put the effort in at school as I did when studying for my ATPL's I might have been in the position I'm in now 20 years ago, so best of luck.
