What to do:
In order to increase oracy levels of students and get them answering questions as productively as possible, try this...
On your whiteboard. When students are to answer any question either you ask them to add, build or challenge or when another student answers a question get them to do that.
Students use phrases such as,
I would like to add to the point X has just made or, I am challenging what X has said, because... or, to build on what X has stated would need...
Use, Try, Refine, Ditch with students too?
Get students to stand up to answer questions, only one person can speak/stand at a time, makes controlling a discussion much easier?