Hi there, when you assign a course, all the lessons are assigned together. However you can follow this method to assign one lesson at a time:
In the classroom that you are trying to assign this:
1. Click the Assign a Course button
2. Select Preview on the course. Don't Assign the whole course
3. Select the Lessons tab
4. Select Assign on any lesson that you want to assign.
This assigns just the particular lesson, and only that lesson should appear in the Google Classroom stream.
You will have to do this periodically as you assign one lesson at a time. We know this is cumbersome but we are investigating better ways of doing this for teachers who want to assign one lesson at a time.