I have two ideas for you:
1) To help you focus: make a tack bra (or just a tack insert, as long as the pins push into your breasts a bit it's fine, it shouldn't hurt too much). Wear this when studying in a public place, and make sure to pick your other clothes in such a way that it would be obvious if you take the bra off. Any time your mind wanders off your studying push or squeeze your bra so the pain can help you focus.
2) For motivation: for every exam result calculate how far your off the maximum score. You will perform a hidden public task based on how many % you scored below the maximum. You can choose how daring you are though!
- Easy: go into a public bathroom and lock yourself into a stall. Masturbate for one minute for every percent you missed.
- Bit more daring: Same as the one before this, but take your top and bra off. Keep masturbating for 1 minute for every 2 points you missed.
- Getting daring: get fully naked, and make sure to pick a stall with a gap below the door so people can see your bare feet. Masturbate until one person has entered the bathroom for every 5 points you missed.
- If you scored really bad you might need something that will help you get these tasks done faster. So you can do the one above in a male bathroom, with the stall still locked, and you only have to continue until one person enters for every 10 points missed.
- And finally: you can also do this in a rarely used (male or female, your choice) bathroom while leaving the door unlocked. In that case just masturbate until you orgasm once, no matter how bad you failed your exam.