I have never been asked what grades I got in High School ever.
That's a tad unusual.
How about
:
- Getting into Uni, you need a good result depending on the course
- Any apprenticeship you will apply for
- Any employment opportunity in private industry
- Any Government role such as Police, Ambulance and public service
- McDonalds
I can't think of anywhere that you wouldn't be asked... other than a trades assistant or basic hired labour.
DJPIL is correct, do the best you can possibly do. Nobody celebrates mediocrity and the one thing you can count on in life is human laziness, so if you can rise above the others that rely on these traits, you have a fighting chance.