If you use Google Classroom there is a good chance you already saw this the last time you logged in. The newest feature allows you to assign things you add to Classroom to only certain kids. Maybe it is something for differentiation, maybe sharing something that someone should read/watch or whatever you see fit.
I added this announcement to a Classroom. Near the top is a new drop down feature.
I can deselect anyone I don't think needs or could benefit from what I am sharing.
There are a million uses for this.