From Teachers Pay Teachers:
Many of us work with students who struggle with group collaborative assignments because of their difficulty with social situations. One strategy that I have used to help students participate successfully in small groups is to assign roles explicitly to the participants in the group. These cards provide a fun way of doing it. You can mix them up and have the students draw a card or you can assign the roles depending on what works best for your class. Cut them out and laminate them or leave them as paper and put them folded in a container for students to draw. I’ve left 2 blank cards so you can add roles that you need for your class that I haven’t thought of. Great for students with autism, Asperger's syndrome, or other special needs.
Here's a blog post on Autism Classroom News for ideas on using the cards.
Here's the link to the cards: http://www.teacherspayteachers.com/Product/Stars-of-the-Group-Small-Group-Role-Cards-Freebie-Autism-624332