Is your school district using Twitter and/or Facebook as an official form of communication? Do you "own" your Twitter and/or Facebook names? Is your superintendent on board?
I think Drupal is the most affordable CMS system around. I just got my twitter feed to post to the front page of our webpage. This means that using the Twitter webpage, my school secretary, magnet coordinator, principal, and counselors can post updates on school activities. If there is deeper information, they can post a link to the google calendar, where the information can be added in a similar fashion. Using web2.0 features also improves my schools Texas StaR Chart annual technology survey. Twitter is a great resource if it posts to a schools website. It makes the user interface "fool proof" and can proliferate info to mobile devices, facebook fan pages, and twitter accounts simultaneously. I'll post a link to my drupal website when it goes live in a few weeks. examples of our twitter feed though: http://twitter.com/debakeyhigh
Also, Pew did a great study on Twitter/Facebook usage: http://www.pewinternet.org/Reports/2009/Twitter-and-status-updating...