How I Use It
I use Twitter to keep my students informed of upcoming classroom events, as well as reminders to complete homework or prepare for upcoming classroom activities. Additionally, I allow my students to contact me through Twitter (using an @reply, never Direct Messages) outside of classroom and school hours for additional help or explanation of assignments as they are working on homework. My next step is to allow students to live tweet the occasional classroom session to enhance their learning experience during school hours.
What makes Twitter such a valuable teaching tool is the diversity of how it can be used. Mainly as a mode of mutual communication, it can be used for additional "office" hours, reminders and announcements, professional collaboration, running a live tweet hashtag stream of classroom learning as it's taking place, not to mention using the tool as a meta-communication tool- allowing students to create fictional accounts relating to characters of study (i.e. "John Proctor" from the Crucible) and create group tweeting experiences that enhance the traditional learning approach in the classroom. (for other ideas, see: http://www.teachhub.com/50-ways-use-twitter-classroom)