If you discover that student/s screen/s are not showing up on your teacher device check a couple things on the student device:

1) Make sure that the student's chromebook is up to date. You will either see an up arrow in the bottom right hand corner near the clock or you will need to go into settings under "About Chrome OS" and check for updates.  Restart the device and have the student login.

2) If it continues, make sure the student is connected to a student wi-fi (not MV-BYOD).  

3) If this issue continues, follow these steps:
1) Choose your class
2) Go into Class Settings
3) Select Ad-Hoc
4)Select the correct duration of your class
5) Click on Start

4)If the problem continues, reach out to me and I will work on it for you.