No one knows, because all the creatine users are working on their pecs rather than taking exams.
A pubmed search reveals:
Benton D, Donohoe R. The influence of creatine supplementation on the cognitive functioning of vegetarians and omnivores. Br J Nutr. 2011 Apr;105(7):1100-5.
Rawson ES, Venezia AC. Use of creatine in the elderly and evidence for effects on cognitive function in young and old. Amino Acids. 2011 May;40(5):1349-62.
It appears that cognition in the sleep-deprived or elderly can improve cognition by a small amount.