I'm not sure where you received your information, but many SM children do speak
to their peers, or at least a select few.

My own daughter with SM from age 5 to 10 spoke to every child in her class and
those in her school in older grades. As well she would go to the park,
playground or stores and just walk up to children she had never met before and
strike up a conversation. With adults she spoke to no one except her parents,
not even her teachers whom she adored. Anyone who was a teenager and appeared
to her to be an adult was not spoken to. Some teens she would easily speak to,
it seemed to be that she just couldn't speak to any one who might be an adult.
As for not completing homework, this may be because there is something your
student doesn't understand and just can't bring himself to ask anyone. He needs
to have a way to ask questions and participate without any pressure put on him
to speak and without feeling that he is being centered out.

Julie
follow your heart