I think Nootropics would be what you're looking for, SNS carries a wide range of these, as suggested by Fightback, I'd check out FocusXT, we have tons of reviews from people specifically using it for exams and enhanced concentration...an overview...
Focus XT Summary of Benefits:
Improved Mental Focus, Concentration, Clarity, and Alertness*
Improved Mental Performance, Memory, & Cognitive Function*
Maximized Energy Levels*
Improved Stress Levels*
Improved Athletic Endurance, Drive, and Motivation*
Improved Ability to Train More Intensely for Longer Durations of Time*
Improved Sense of Well Being*
Pre-Workout or Pre-Athletic Energy and Focus*
Improved Mind-Muscle Connection*
Combating Overtraining Syndrome*
Increased Fat Burning During Exercise*
Link to the SNS products on Nutraplanet...
http://www.nutraplanet.com/manufacturer/serious-nutrition-solutions/
Let us know if you have any questions!