If either of the students that are assigned to the chair are busy working at their desks, other students can sit in the chair for the time being. I just tell them they need to ask the student whose day it is.
One day one of the boys came up to me. He was done with his assignment and was going to read. The girl whose day it was to sit in the chair was busy working on a project with her group on the other side of the room. He came up and asked me if he could sit in her chair since she wasn't. I told him he needed to go ask her if that was ok.
A few seconds later he came up to me, seeming a little annoyed. He said, "She told me that I needed to come ask you if it is ok." I laughed and said, "Yes, that is ok with me." Then he said, "You guys are just like my mom and dad. Go ask your mom.... Go ask your dad....Go ask your mom..." As he walked away from me, he was still muttering under his breath, "Go ask your mom... Go ask your dad..."
Poor kid. But I couldn't help but get a good laugh out of it.