You're kidding youself if you think it doesn't work, ofcoarse it does! It's given to people to increase attention span and INCREASE CONCENTRATION.
do you need it? no
is it bad for you? in high enough doses, yes.
does it work? damn straight it does!...it makes me actually want to study.
To the OP, I dont have ADD or ADHD but I take it whenever I can get my hands on it, and took 10mg about 20 minutes ago. First up, it gives you a rush of energy, makes you feel on top of the world. Then about an hour after you take it, you'll start to lose that energy, but the concentration still stays. The more you take, the more energy you get, and subsequently the worse you feel when you 'come-down'. Take too much, and you'll be anxious/moody later on in the day. Don't expect to feel hungry either.
So yeh, it definitely works, but it has its negatives too. Awesome stuff for cramming though.