Hmmm... not sure if anything is "unique" or not, but my daughter skipped year 3 and is currently in year 4. In terms of maths, I would say the biggest "step up" (and it's not overly large) is in:

* mental maths and computing speed
* division
* geometry (using a compass, more indepth exposure to more complex shapes and angles)

That's about it smile jojo