It is unknown why except that it may be a form of comfort. Autistic children especially have repetitive behaviors. Sometimes they are involuntary movements and are labeled dyskinesias. choreoathetosis is a term describing movements that are brief, purposeless,writhing and blend in a stream of movement.
Wayne Yankus, MD, FAAP
expert panelist: pediatrics
It has been my experience that some children "rock" for a variety of reasons including: calming themselves, helping to integrate and adjust to changes of stimuli in their environment (such as loud music that can agitate some children), habitual reasons (like to repeat the movement and have a need to be perseverative) or for enjoyment. Sometimes rocking is paired with vocalizations, too- such as humming.
Not all children with learning challenges rock, including those with autism.
Thanks for asking your question-
Louise Masin Sattler, NCSP
Nationally Certified School Psychologist
Owner of SigningFamilies.com