>this affirmation makes me remember an Einstein story:
>
>Einstein was to pass the same test of last year for his students.. his assistent asked if was smart to use the same test for the same group.. He answered: "the test is the same but they are not the same.."

I had a case like that, accidentally, while I was teaching. I had scheduled three tests on the same day, but forgot about it and prepared only two. So I repeated the second one for the third group, counting on them not expecting it to be the same, and being in a different wing of the building.

They all failed, because the one guy who knew some maths had a flu, and he was the only cheat sheet they had :). They weren't taken aback by this, saying they expected me to repeat the test, as I obviously gave them a harder one than to others. When I told them they actually had the same test as the second group, they acted diversely... some rolled their eyes, some sighed in resignation and some slapped their foreheads.