Well, not really, in my experience. I left high school after grade 9 and went into a correspondence college. So you don't even need a junior certificate as far as I know (gr 10) - at least not in SA.
However, if you want to go back in to a school after having done a year or so of correspondence, then some schools might request that you repeat the grade. IE. if you did grade 10 via correspondence, then if you go to say a public school, they would make you repeat that grade instead of putting you in a higher one.
I'm not sure about a private school. Generally private schools are more accepting of part-time students, I've found.
This is all just taken from my personal experience with the matter. Sorry I didn't answer earlier, w@cko - I thought I had to make a hub out of this thing, but it turns out I don't. :)