The difference in scores is accounted for by the different motivation of the two test takers.
Step-by-step explanation:
The person who scored less than their mate who they believe to be considerably less intelligent than themselves is obviously feeling imperceptive and thus wants to prove their intelligence.
Meanwhile, the other friend has been negatively reinforced and forced to take a test he has already done well in, so he has no motivation to do it as good as he may have done before when he genuinely wanted to performs as good as he could.
So the person who scored less scores more that their previous and the person who scored more scores less.