Just ran across this article and thought of this thread. Hope it helps you sort out what is going on:

Is It Really ADHD? Or Could Your Child Have a Learning Disability?
Your child was diagnosed with attention deficit disorder, and is taking ADHD medication, but he's still struggling at school. Could a learning disability be to blame? Learn the warning signs, and what parents can do to help.
by Larry Silver, M.D.
http://www.additudemag.com/adhd/article/3270.html