I would look at:
Developmental Coordination Disorder/Developmental Dyspraxia
Sensory Processing Disorder (esp. visual and auditory)
ADHD
These three things tend to go together so you may be dealing with them all. Wikipedia has a good page on Developmental Coordination Disorder.
My DD is exceptionally slow with processing when she is not medicated for her ADHD but "almost" normal when medicated. For instance if she is not medicated and I ask her what is 10-7 I might get a blank stare but she answers within a second when medicated.
