Shawna,
I am newer at this, and I've tried emailing the students reminding them of the chat, as well as posting announcements in the classroom. After the chat I send a 'thank you for participating' email to those that participated, and a 'we missed you' message to those that didn't. While I've tried all these things, my attentence is around 5 out of 30. I'm open to suggestions.
