In America at least, if a grade school student (K - 12) is exceptionally gifted they are allowed to advance to a higher learning level without having to take the previous courses, up to and including entire years.
Has this ever happened in the wizarding world at any school?
As far as Hogwarts goes, Hermione would have been a good candidate, but I don't think she ever skipped ahead at all. Riddle and Dumbledore would also have had the capability, but I'm pretty sure Riddle went through all seven years' classes. I don't know Dumble's history.
Again, I'm asking about any and all of the wizarding schools in the world. Whether any student has ever been able to skip a whole year or even a couple classes due to their talent.