In my online class lecture, I've found a few techniques to engage students in discussion. It can be easy for a student to just log in and look like they are attending the chat without actually engaging the chat. So, I always acknowledge students and greet them by saying their name when they enter the class. I also make sure to call on individuals to answer questions, rather than asking a question to everyone. This controls the responses as well as engages the student at an individual level.
