An auditory processing delay is a neurological defect that affects how the brain processes spoken language. This makes it difficult for the child to process verbal instructions or even to filter out background noise in the classroom. While their ability to hear is ok, there is a neurological basis for their impaired ability to listen.
A child with auditory processing delay can often have the same types of behavioral problems as a child with ADD. However, using the techniques appropriate for an ADD child will not be very effective with a child suffering from auditory processing issues.