I have noticed over the years that there are two ways that students look at me in class.
When I am using English they seem far away. They seem to be considering what I’m saying but not really caring very much about it. I guess they hear enough English.
But when I’m talking slowly in French about them in a way that they can understand (i.e. using Walk Before You Talk, going ten times slower than I think is acceptable, pausing, listening to them, looking at them and really seeing them), then their their demeanor changes.
They don’t slouch as much. Some move up to the front of their seats. Many of them have those slight smiles of understanding on their faces. They seem interested.
I prefer the latter way to interact with my students in class. I prefer the way of personalized non-targeted comprehensible input.