I think its less about the dolphines than the fact that when you give a spectrum child an activity they absolutely love - in that, peaceful, all-is-right-with-the-world way - it is really helpful. Some spectrum kids do really well with horse therapy for the same reason. For my son, its hiking in complete solitude. I am so glad we found a key for him that is 100% free 
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).