Question: do you have problems concentrating on problems or subjects which _really_ interest you? I've worked with a lot of kids who can't wrap their brains around read 'n test work-sheet-style school activities, but just fly when given a problem to solve that is practical and of interest (and, just by the way, involves using the same skills that the worksheets use).
You may well have inattentive ADHD, but you may also have a different learning intelligence or learning style than standard. In other words, you may absorb information just fine, but the method that works for you is not the one that they use in school. Here is a real basic page on the characteristics of visual, auditory, and kineasthetic (tactile) learners, and what teaching approach works best for them. See if you fit into one of those categories.
http://www.familyeducation.com/artic...,4-605,00.html