I feel it is important that all students ask questions. For those students who may be afraid to ask questions during a lecture or activity for fear of feeling "stupid" I would use notecards and a Q&A box much like a suggestion box. The process though was mandatory for all students in the class. Each student had to submit a card at the end of the class period and each question would be reviewed at the next session. This served as a method of review and allowed for the individual who thought they had a stupid question to ask the question without fear of being made fun of.