It is very common to have a learning disability along with ADHD. In fact, research shows that thirty percent of people with ADHD also have a learning disability. Beyond learning disabilities, over fifty percent of individuals with ADHD have some other type of brain-based disorder. This is why depression, anxiety, OCD, bipolar disorder and other similar disorders are higher than normal in ADD clients.
One type of learning disability that almost every person with ADD will have is an integrative processing deficit. This is the ability to take in information, process it quickly and make use of it. Most people with ADD are either slower than others in doing this or have trouble doing it at all. It is not that they do not understand the information, but conflicting signals will make it difficult to fully process.
Another common learning disability in people with ADHD is working memory problems. Working memory is another term for short term memory, or information that is told to you in the moment. This can affect information you hear, read, etc. Working memory is important for doing well academically and in your work.
Another learning disability that is common in ADHD clients is problems with visual/spatial processing. This is not too surprising since most people with ADHD have problems with organizing space. Academically, this will affect subjects such as geometry and physics.
Other common learning disabilities are dyslexia, reading comprehension, arithmetic reasoning, oral expression, written expression, foreign language acquisition, syntactic processing and most likely other learning disabilities. This is why getting a thorough examination at the start is so important. An individual may be dealing with ADHD, but he or she may be dealing with a learning disability as well. And though you cannot directly do anything about a learning disability, it is good to know you have one and how it affects your ability to function. Also, you may receive academic accommodations as well as job accommodations if diagnosed with an LD.
In order to find out if you have a learning disability, it will be necessary to go through a lengthy set of tests that compare and contrast your IQ, personality and interests. If you do significantly better on one aspect of a test than another, this could signify a learning disability. For example, if you do really well on the verbal part of your IQ test and not so well on the visual/spatial section of the IQ test, you may have a learning disability.
It is not known exactly why ADD often comes with some type of learning disability. Most likely, the atypical wiring of an ADD'er has something to do with it. New research is being done every day on the brain and how it works, and science definitely does not have all the answers to these questions yet.