I was decidedly mediocre... Not quite top set, but next one down. Did fairly badly in 'A' levels - have a poor memory, but then found my subject at uni, loved it, got a 2:1 and became a teacher... which makes me smile as my teachers always told me at my mediocre comp that I'd never get my GCSEs to be a teacher, so I should give up the dream and do a BTEC in admin and work for the local bank!
Hubby on the other hand, was v bright... assessed for gifted and talented etc etc (way back in 70s before it became popular). However, he was a lazy little git and bummed out of his A levels twice. Finally, now in his thirties he is getting his degree.
Intelligence is only part of the story I think, hard work, memory, learning styles, subjects and teachers all play their part too!