Nieva,
Domineering students can certainly be a problem in online classrooms; although I don't believe they stiffle participation as much as they do in the traditional classroom.
My general rule is... praise in public, reprimand in private. If I feel a student is dominating the classroom discussion, I will send that student a private email or, better yet, call them on the telephone. I generally take the approach... "I have a problem...can you help me solve it?"
Too much involvement is much easier to solve than too little. :)
Thanks for your input, Jane
