The basic proposition is that since ADD is a neurological disorder, specifically a brain problem, then in order to deal with the problem you have to change the brain. Normally this is done by administering Ritalin, but that can have some ugly side effects, and besides parents will sometimes wait to dose the kids until the kids are home, since the parents (understandably) want some peace and quiet too. Biofeedback trains the children to increase the beta waves -and thus their concentration - while reducing the theta waves. It takes a while to get the effects you're looking for, but when you're done with the biofeedback therapy you have a kid that's better off than if you'd gone with Ritalin or some other stimulant. Check this article out.
Lois and I tried a number of things with our son - diet therapy, Ritalin, conventional therapy, and other brainbending drugs. Odd that it never occurred to us to try biofeedback, considering Lois' long time interest in higher consciousness/altered states and my experience with my little brother, which made me suspicious of drug therapy.
I have some other thoughts on modern school environments and how they might be aggravating or producing EBD/ADD problems in kids, but that's fodder for another post since I need to get cleaned up and get rolling.