By Tomasz Pilch, Poland
In large classes (and here in Poland they never exceed 30) I would manipulate the material so that it would have the form of students interviewing students about information that afterwards they will be asked to report to the class.
As a result, during the first part of the assignement there is such a noise (because there are up to 15 pairs of students talking to each other at the same time) that even shy students do not feel embarassed by the situation and find it quite easy (I gather) to speak.
Afterwards, if the task permits, I ask two students from different groups to report on what they have learnt from their interlocutors and then one student to try to tell us what in the views/opinions presented before was similar and what different from what his/her interlocutor said. This way you have students use direct speech and then reported speech, plus gathering information, reporting it and making contrastive comparison - during conversation classes it works well, much better than teacher to students exchange, which usually ends up with teacher monopolising the class time.
I also ask students to prepare questions (or whatever the task requires) and then choose the person to answer/respond, then the latter takes over and asks question to a student of his/her choice (thus they never know who will be asked and therefore pay attention).