"Surprisingly, despite the widespread infusion and use of the Internet, we have yet to develop a clear understanding of the impact these technologies have had and are having on the processes of learning. Theoretical and research foundations have not kept pace with technological growth and use. Several questions have been posed and answered; yet many more remain. We are developing a good idea of 'what' the technology can do, while 'how's' (e.g., How can the Internet assist us with teaching and learning processes?) and 'why's' (e.g., Why this technology now?) remain relatively unclear." So say Hill et.al. in a chapter of the Handbook of Research on Educational Communications and Technology.
Anyone who teaches online and in face-to-face classrooms knows that the each environment poses its own challenges and opportunities. It's a mistake, however, to treat them as if they were the same. Distance has an effect on teaching, and "distance" can be defined not just geographically but psychologically. Perceived distance between instructor and learner has to be minimized. In the physical classroom, the teacher moves toward the student, walks around, focuses visual attention, invites students to share. Online, distance is shortened in similar ways: by calling on students by name, "poking" them with public and private messages, inviting interaction, and sending emoticons.
Control of the traditional classroom is accomplished via physical and visible measures: the instructor metes out harsh looks, raises or lowers the volume, raps on the table or chalkboard, etc. Online, control often transfers to the learners, and instructors have to make difficult decisions about how much of that control they want to relinquish. Turning off chat, for example, can help ensure that students will not be distracted from your whiteboard content, but it may have the negative effect of making them look elsewhere for opportunities to communicate. Ruth Clark laments that "lacking the physical presence of the instructor, student attention in the virtual classroom tends to drift. It’s not uncommon for participants to respond to email, review unrelated documents, or even leave their computers during the session.” J. Pulichino, in The Synchronous e-Learning Report for 2005, maintains that “the main frustration with the virtual classroom environment is multitasking. No matter how engaging you are as an instructor, you must still battle the students’ constant temptation to check email and multitask.”
The social context of the physical classroom is determined by the physical presence of other students and the instructor(s). Online, students can't always see or hear one another (unless the instructor makes that possible), so they may need to be assured that there is a "there" there: that others are a part of the online class and that they share a common "space," even if they can't see it. Audio feedback - at least of the instructor's voice - cannot be over-emphasized in this context: it's the single most effective reminder of presence. It's also a good idea to make sure students are comfortable with the online environment: that they can navigate between the panes (chat, whiteboard, roster, video window, etc.) easily and are comfortable with the online classroom so that they can find and appreciate various other indicators of social presence.
How do you make your students comfortable in your online space?
 Clark, R. C., and Kwinn, A. The New Virtual Classroom: Evidence-Based Guidelines for Synchronous e-Learning. San Francisco: John Wiley & Sons, 1007, p. 57.