I got an A at O-level about 150 years ago
Maths was by far my best subject at school, but DCs bring home lots of (primary) homework that's a mystery to me and of course even when I think I know what to do modern methods are different to the ones I learnt (and it's all a bit rusty).
I'd be happy to give a fair bit of time to the study, but would prefer to work through the books myself rather than do a course. Is that realistic?
How do I find out which books I need?
How do I get entered for the exam if I don't do it through a school/college?
What happens about course work? Is there any in GCSE maths these days?
When is the soonest I could take the test?
How much study do you think it would take?