While ADHD is a disease of focus and planning, Autism Spectrum Disorder is an illness of impaired communication skills.
People exhibiting Autism have great difficulty analyzing a person’s body language for cues into unspoken meanings. They often break the flow of conversation, by not taking turns and interrupting if they feel they have something they need to say.
A telltale sign of a child with autism is constant averting of eye contact. Paired to exceptionally poor communication skills, this is likely to be a child who has learned to avoid looking into people’s lives because of social embarrassment or shame.
Children with ADHD generally have a better understanding of communication etiquette, as well as the implied thoughts and meanings of others. Behavioral problems stemming from high impulsivity/hyperactivity can also cause them to interrupt or act hostile, however.