as admin check your server has jabber set up. type jabber in the site administration search box to get there. As a student complete an assignment (online text is probably the easiest here). Check the students messaging preferences to make sure they will receive assignment notifications via jabber regardless of whether they are online or offline. If the jabber column doesnt display put your jabber id in the jabber id text box and click update profile. As a teacher grade the submission. Wait "maxeditingtime" minutes. max editing time is a server setting. Run cron (/admin/cron.php) a meaningful jabber message should arrive.