Here is a message that I email to the students (and their advisors) in the second week if there has been no participation in the class.
Subject: Welcome to the Class!
Welcome to the class! We will have an exciting xxx weeks, and I just wanted to send this quick note to remind you that due to the accelerated nature of this course it can be challenging to catch up if you fall behind. I want to see you do well, so be sure to read the “Hints†announcements that I will each week, and of course if you have any questions please don't hesitate to contact me via email. I am sure that together we will figure out "what needs to be done" so that you excel in this class!
School is an exciting time, and going to school is not easy, but the long-term benefits and the unbelievable sense of accomplishment when you are done will prove to you that you "did the right thing!"