I'm about to complete me GCSE Maths and Physics. I hired a tutor who sent and marked assignments, bought second hand textbooks and cd's online, watched YouTube lectures and found a local college who allow external candidates.
A couple of A*s on your application won't hurt, demonstrates your ability to learn, will prepare you for ATPL studies and will help when you are invited for assessments.
All for less than a grand, which is a bargain if you're willing to pay 55k+ for flight training.
I sit my exams next week and looking forward to putting the text books away so I can crack on with my PPL theory and get some hours in my logbook.