People misunderstand the reason for this. Test takers can improve, but only up to a point, and only because they getting comfortable with the test format, not because they're getting any smarter. Solution: give the candidates a few practice tests first.

This extends to every test though. My ACT score jumped massively on my second try. The reason: I didn't realize how much little time they gave test-takers, so I ran out of time on some portions. The second time around, I rushed through as fast as possible.