Please help! What are some inexpensive, but effective ways to help my child?

My son has ADHD. He’s on medication, but it doesn’t seem to be working because his grades are declining drastically! Don’t get me wrong, I’m not so naive to think that there is some magical pill that will automatically sky-rocket his grades from failing to straight A’s. But at the same time, I don’t know what else to do in addition to the medication. He struggles with simple mathematics, has a very short attention span and he has a horrible time focusing on just one task. I try to work with him as much as a single working mother can and it does no good. He has an excellent teacher who also spends more one on one time than she has with him also. When I take him back to see his pediatrician, I’m going to ask for an increase in his dosage (as much as it pains me to see him on it) and a referral to a child psychiatrist – or a psychologist? In the mean-time, what can I do? I don’t want to see my child left behind. Just like any parent I want what’s best from him. He’s my only child and I don’t claim to be the best mother, but I do what I can. Some of you are way more experienced than I am. HELP!