To help students that are too shy in class to speak up, I will put the students in discussion groups. I will then ask a question and give them time to discuss it among themselves briefly. Then one student can answer for the group. I find that this sometimes allows the shy student to build up their confidence first in a small group before they are ready to respond to the whole class. I have found that as the class progresses, that shy student tends to participate more as a whole.
