The professor is also willing to discuss issues and answer any questions. I feel that the biggest responsbility for students to establish a learning community is to ask questions. Any question, about anything related to the material presented to them. I recall that one of Richard Jacob's goals of IGE is to encourage people to ask questions and he makes sure he establishes some material that will get even the most quiet student to ask. In many classes, I witnessed that asking questions stir conversations and make seemingly-borning stuff intersting.
Questions are a sure-fire way to let students learn from each other.
The professor is also willing to discuss issues and answer any questions.