I teach math courses at a career school and frequently have students who have math anxiety and lack confidence in the subject. I encourage questions from them by giving them examples of math questions my friends ask me. That way I help them realize that I am open to any level of question. My goal is if people in my life are comfortable asking me a basic question, students should not fear asking me a question. The other thing that I always allow is people to mouth the answers or use fingers and gestures to indicate their answers. After a student does that a few times and realizes she/he answered correctly, verbal answers and more questions follow.