In recent studies, there have been a couple of natural remedies that seem to help ADHD symptoms.
One is the powerful anti-oxidant Pycnogenol, which is a kind of pine tree extract. A test was done to see if this anti-oxidant would alleviate ADHD symptoms in kids, and it did! There are no known side-effects at this time.
The other natural remedy is fish oil - which contains omega 3 and has been proved in Australia to improve a child's attention span, and has no known side-effects.
So, take a look at the above studies, and see if this could help you or your child with ADHD symptoms.
(Make sure to only try one of these remedies at a time, as Pycnogenol is not supposed to be taken with some other vitamins.)