[demewmew]

In my experience the decrease in performance can be felt both short-term (the classic example of students taking a standardized test) and long-term. It also doesn't necessarily mean that someone is doing poorly - they may just be aware that they're not performing at their potential.

[cantastoria]

If someone is consciously aware they are not performing at their potential and continue to do so, I find it hard to lay the blame at the feet of stereotype threat. No? It sounds like they're either misjudging their potential or just being lazy.