How you're likely to be affected by it could depend on the time of day at which a test is taken, seemingly.

Clearly, the human brain is at its sharpest after a good night's restful sleep ... implying that the earlier in the morning you sit a test, the better your performance will be (assuming you've prepared adequately for it beforehand, of course). According to a study of 2 million tests taken by Danish schoolchildren, researchers found a decline in scores for every hour after say, 9 o'clock ... putting the difference down to what they referred to as "cognitive fatigue". Whereas, ... tests taken *after a 30-minute break saw scores improve. Although the reason(s) for *this is/are yet unclear.

There again, the same principle applies to tests taken in the afternoon - the earlier the better - leading to Henrik Sieversten of the Danish National Centre for Social Research in Copenhagen to believe that children's mental resources are recharged following a nourishing lunch combined with fresh air.