I suspect he is playing with the answers deliberately. Over the last few months he has taken to calculating the minimum grade he needs on a test to carry an A in class, and then hits it.
OHG, your comment made me laugh as I remembered something one of my economics professors said. He told us in order to use our resources (e.g., time, energy) efficiently, we should only be working hard enough to get the lowest possible scores that would result in an A. He said since an A is an A on a transcript, and there are no A pluses, why waste your time working harder for the higher scores? (My answer was that we should be there to learn as much as we could, and not just to get grades.)
Maybe your GS is destined to be an economist!