On one level, Dyslexia and ADD / ADHD would seem quite different, but in reality, we are only at the beginning of our understanding of how the two might overlap and be different.
Both Dyslexia and ADD / ADHD were initially characterized by their negatives – Dyslexia by difficulty learning to read, and ADD / ADHD by difficulty paying attention. Today we know that for both, positive qualities like higher levels of creativity and ability can be associated as well as negatives, and researchers are only now beginning to take a more careful look at what these two designations imply.
For those who don’t know, as a group, children with ADD / ADHD score lower on many tests of phonology and reading comprehension, theoretically because of their great demands for attention and working memory. Children with dyslexia are usually identified by cognitive and academic testing whereas students with ADD / ADHD are identified by parent and teacher checklists.
In the US, the incidence of dyslexia has been estimated to be 10-17% of the population, whereas ADD / ADHD has been estimated to be 5-10%, so a high co-occurrence might be expected. However, dyslexia and learning disabilities in general are often unrecognized because of low levels of awareness and financial burdens of testing. In one study of an outpatient pediatric psychiatry clinic, 24% of children had an unrecognized LD (Sundheim and Voeller).