I have to say, the first time I worked with autistic children and yoga was very challenging. The children were a mix of levels on the autistic spectrum - some more aware and more verbal then others. So obviously, some were more involved then others. I had worked with this same group the year before engaging them in a How to Draw lesson, so I knew the extent of their abilities. Throughout the drawing lesson, one child in particular had stared off and preoccupied himself with the repetitive movements that are common among those with autism. When the lesson was through, he picked up his pencil and drew the entire picture I had taught them, with added background details. I was amazed. So going into the class to teach them yoga, I knew that even if they may not be participating, they are most likely absorbing what is happening. Perhaps they take those skills home with them and practice them in their own time in their own way. However they get there is beautiful.
I was only able to spend one afternoon with these children, but working with an autistic child over time through yoga can have huge benefits. For instance, the inhalation and exhalation of breath work alone can become the repetition that takes the place of the well known "flapping" or rocking as the additional oxygen calms the nervous system. Child's Pose can become a safe way for the child to shut the world out lowering the overload of visual stimulation and avoid meltdowns by bringing internal focus. Seated Forward Bends can provide self control while helping fulfill that need for deep pressure. Engaging the children in rhymes with repetition and animal sounds with the asanas (mooing in Cow Pose, barking in Downdog, etc.) is a way to get on their level. Stories and bright pictures also stimulate attention. I used the book, "My Daddy is a Pretzel" and "Whoosh Around the Mulberry Bush" incorporating the poses through Storytime Yoga.
There are so many ways and techniques to integrate yoga into an autistic child's life. Check out some of the great resources on this subject and broaden your awareness.