Can admin set the default role of meeting participants to attendee instead of presenter?

I have the exact same problem with dahgijsbers ... and my situation maybe even more complicated as most of us need to start lesson in private channels, in which scheduling is not possible.

Our initial deployment is using a subject-based Teams and class-based channels inside. To make things like normal lessons, teachers are required to hold the meetings for their own class. With our initial deployment, as every lesson in NOT visible to all the team members, scheduling for channel meetings seemed not possible, so teachers need to "Meet Now" in respective channels; and in this way, they could not set the "Meeting Settings" and thus could not choose "Only me" in the "Who can present?" section. However, it is really labor intensive for colleagues to do so manually during lesson, since some would need to hold lesson with about 100 students at one time.

I tried to update the "Sharing content" policy for students so that sharing screen shall be "Disabled" for them, but testing shows that the student applied with the policy can still share his screen... so any way out apart from telling student to behave themselves?