If you want to ensure your participants will be able to share their screens within a Zoom meeting prior to starting the meeting, there is a way to do this through Zoom's meeting settings
Log into Zoom
First, log into Zoom at snc-edu.zoom.us. If you have questions on this, refer to the following article:
How To Sign In To Zoom
Navigate to Settings
Click on Settings in the left menu bar. 
Click on In Meeting(Basic)
Scroll down until you find the Screen Sharing section. Click the All Participants button under Who can share? to allow allow any participant in your meeting to share their screen.
Additional Resources