How can I encourage participation and interaction of withdrawn or shy learners with their peers and myself (the teacher) whilst in the classroom?

I teach music business to musicians and usually the students I get are very confident as they have been performing as a musician or have come directly from school and they have come out of their shells. During the first session I asked all my students to come up with a question for the rest of the class so they could show off what they had learnt from the previous 12 weeks and one student couldn’t think of anything. I asked her to tell me one thing that she learned instead and she just said her “brain had frozen”. During the lunch break I decided to have a quiet word with her and she explained that she was really shy and didn’t like answering questions in front of the class. This was something new for me as I believed that I was quite good at spotting the shy, withdrawn students from their body language and their tone, however this particular student comes across as being very confident which has made me think that there are different elements of shyness and I want to know how to spot them and how to deal with it.

I want to research and develop strategies for dealing with shy and withdrawn students so that they can become a bit more confident and so that they don’t feel awkward within the class. I am interested in finding out why some students are very confident in the classroom and will communicate freely and why others don’t.