But executive function issues are also huge in Autism Spectrum Disorders (ASD) too
Absolutely.
Malika - yes, we're talking about the same thing. What they are describing is a symptom of sensory integration problems - especially midline processing. It has a huge impact on things like writing. The ability to simultaneously manage each side of the body separately, Know what I mean?? It's why my difficult child does better playing a band instrument, than playing piano. On a band instrument, both hands work TOGETHER... on piano, they work independently (especially if you're playing a Bach Fugue). Writing... one hand manages the paper, the other manages the pen. Affects a lot of other things, too - those are just easier to describe.
"Tapping" and ADHD do go together... it's part of the restlessness, the impulsivity, and self-"medicating" (the independent activity actually helps the kid focus - some kids listen better if they are walking/running on one spot, than if they are trying to sit still).