I have observed various forms of talk in my classroom. Every morning my CT or one of the 402 students reads a book to the class. After the book is read students have the opportunity to ask a question or say a comment. The students are allowed to say whatever they want and my CT does not facilitate any discussion questions herself.
Another type of talk I have observed is when the students do their morning journal on Monday's they brainstorm ideas as a class and my CT writes them on the board. This helps students who may have a hard time remembering what they did the previous week. This also lets those students who actively always want to participate to have a productive way to participate in class.
There are a few students in the class that have a problem with blurting out. These students need to be scaffold on how to participate productively in a conversation. There are also a few students who are ESL learners. You can not tell by listening to some of them speak but it is more evident in reading.