No comprehensible input class – especially one organized around unscripted, authentic communication – can succeed unless the students and the teacher are trained from the beginning of the year in the art of negotiating meaning.
In the same way that we don’t allow students to pick the character, if we are using the Invisibles/emergent targets approach to teaching using comprehensible input, so also do we not allow students to drive a story before it happens. The process of creating a story is an unfolding process of negotiating meaning as a group. It happens quite often that a student will start rapidly sharing with us in English, sometimes right in the middle of class, their vision for the story. No blame. They are children.
In an extreme example of this phenomenon, once two of my students got together and wrote out a script for story, explaining to me that that was our story for the day. I had to explain that, like life, stories cannot be planned out too much or they will be boring. I explained that anything they wanted to see in the story had to come from their own good efforts at negotiating the facts of the story with me and the rest of the class during the story. I say that to my students all the time.
If a class wants a certain celebrity from the pop culture in a story, then they need to find the place in the French discussion to fit that celebrity in without using the L1 and knowing that it is not their story but our story. If they want their ideas in the story, they must learn to negotiate meaning with us as we narrate things along. To do otherwise is not a true conversation. So, students are not allowed to wave their hands or blurt or squirm around in order to get their idea heard.
Indeed, the underlying principle of any classroom based on comprehensible input has to be that of negotiating meaning. That is what language is. One person, usually me, says something, and as soon as I say it, the class and I must work together to negotiate what I said, and then the class returns the ball to my court, even with such a simple response as a yes or no, and the story develops in a back and forth way like that.