Meet with a student class

Today I listened a class meeting with a teacher and 25 students.
The students can use a private chat each others during the lesson. Is there a function to disabled this tool? The teacher can’t see these chats, so I think the better way is to disable the tool and permit only a public chat.

If I may, the students will just use SMS or Snapchat or any number of tools to communicate privately if that option is disabled. This feature might not solve any problems within the class.

I know but we can begin with this function disabled and at the same time the student have to use only the desktop with the lesson.