Does the school have a policy against any kind of messaging behind students during Zoom calls?
If so, then this is appropriate, to prevent distraction. But if not, it would have been a fabulous teachable moment about free speech.
Ah, it appears the school does allow these kinds of expressions:
“The Board respects students’ rights to express ideas and opinions, take stands on issues, and support causes, even when such speech is controversial or unpopular.”
The teacher was wrong. And should have taken the opportunity to have a brief lesson about free speech.