Writing Workshop

It seems to me that it is almost assumed that a child will want to share her work with the class. It was said in the book that writing was not a choice. The child has to write in the workshop. However, nothing was said about sharing. Do children have to sit in the authors chair and share with the class if they do not want to? It seems that this is a very important aspect of the workshop. It seems beneficial to the authors and the students to critique and have their work critiqued by their peers. I know sitting in the authors chair is helpfull, but is it necessary for every student?