My son happens to have all three of the "D's" of learning disabilities, so I am all to familiar with them. However, many people are not. They are dyslexia (reading problems), dysgraphia (writing problems) and dyscalculia (math problems). I recently learned that approximately 10% of the population have learning disabilities. I came across this post that explains them all in layman's terms. The NCLD (National Center for Learning Disabilities) is also an excellent resource to learn more about each.