whataboutthemenses asked: (2/2) wouldn't ask them to start doing algebra. If you can ease them into presenting to two students, offering up answers when you call on them, having a discussion for participation marks with you in private, they might get a little better at discussion. Also try setting up a chatroom for discussion, or something like that - give them the opportunity to participate in discussion without having to be on the spot.
Thank you so very much for your insightful and thoughtful comments. I have chosen to offer verbal and written participation points with the hope that over time some of the more non-verbal students will share out. The student in question actually did talk in class today! Thanks again!