The symptoms of autism are hard to define because each autistic child is unique in their own way. Not only are the symptoms individualized but the severity of the disorder also differs from child to child. One child might have mild autism and be able to function normally at home or in the classroom. The only difference you might see is minor social awkwardness when interacting with other or a certain preference of where there food is positioned on a plate. On the severe side you might see a child that has no communication skills. They are impulsive and their behavior, though no fault of theirs, borders on one that is socially unacceptable. Some autistic children have no fear of social norms.

One of the symptoms of autism is a delayed or unusual speech pattern. When young severe autistic children will grunt, stutter, or talk slowly with long breaks between each word or syllable. Mild autistic children have been known to memorize entire books or scripts from a television show. There was a case in Maine where a teenage autistic boy could not tell you what he had for breakfast or what his mother's name was but he could tell you, by cabin, the entire passenger manifest of the Titanic. Other cases have included numbers in their speech pattern. A autistic child in Texas had the unusual talent of counting the number of letters of each word as you spoke them. The count was accurate and immediate, but again, simple knowledge was almost impossible to communicate.

Subtle nuances in language are also a symptom of autism. For example, the autistic child would not understand humor or would find humor in something that was not funny. The emotional reaction to irony or sarcasm would seem out of place and unusual in normal conversation. Physical comedy may be understood by the autistic child, but there actions in both body language and spoken word would seem inappropriate to the situation. When talking to an autistic child, the lack of eye contact is normally seen. They may be listening to you, but their body and eyes are concentrated on something else. You may have their full attention, but you would think that the child was totally consumed by another person or an object that has little significance to you.

The autistic child sometime does not have the ability to imagine anything outside of self. If you asked an autistic child if they would like to do what their friend is doing or how would you feel if that happened to you, they could not put the concept together to compare themselves to the other person or situation. Putting themselves in another's shoes is not a concept they can grasp or communicate. When they do communicate it may seem awkward and inappropriate. They may speak with a very high voice that seems out of place or with a very flat voice that is sometimes inaudible or hard to understand. The conversation, if they are capable will be void of any slang words or words associated in the vocabulary of a person that age.

All these nuances and symptoms of the disorder can be viewed, especially by peers, as being socially unacceptable and divergent of societal norms. Even when playing with others, the other children will have a hard time interacting with the autistic child. This could lead to isolation and further social development unless the interaction is facilitated by an understanding adult.