This was a thought provoking tweet, I found on Twitter.
Avoiding the Trap of "Q & A Teaching" | Edutopia http://edut.to/P2JD4b

It makes sense to make model quick and to the point, with a clear purpose. There is a time and place for asking questions and clarifying. The asking of questions should often be done by the students with you clarify after the modeling is done and the skill has been practiced or when conferring with a small group or individual student. When you are modeling a skill you are often exposing kids to it for the first time and they need it modeled. A good use of the teacher asking questions would be when you give the whole class a problem to solve in any subject where you want them thinking and using creativity and problem solving skills. You can Q & A after giving them time to work on it and the skills needed to solve it have been modeled. Or if you are using the problem as a way to check and see what they know before introducing a new lesson. Q & A has it time and place, don't forget that. There are many places to use it and to avoid it. I am sure lots of you have examples. This was a good concept the think about and they gave some good ideas!