I've been realizing lately that, at least for my kid, the key to perfectionism is emotion. There's nothing wrong with noticing and correcting errors; it only becomes troublesome when anxiety, fear, self-doubt, etc. come on board.
So we've done a lot of talking - and continue to do so - about how making a mistake or being wrong or not knowing the answer in 0.6 seconds is all okay and does not have to hurt. This takes a *lot* of practice, and it's hard sometimes for me to purposely assign things I know he'll struggle with to the point of tears, but I have to keep reminding myself that now is the time to battle this dragon - not when he's alone at college.