I was a kid in an era where people had car phones or big, blocky cell phones. When I was in high school, the thing to have was a pager (for some reason). I never had a cellphone until a few years into college. They weren't even that common right after I graduated from high school.
Just a few years later almost everyone had a cell phone. I've never been in a classroom setting or work setting where I couldn't have my phone.
So there.
Yeah, I'm not sure what that amounts to in France, but here in the U.S. throwing a marker like that at anyone, much less a child, would be considered a battery. And I'd be surprised if someone didn't film something like that on their phone. So, even if the department tried to ignore it, they'd be forced to respond in some way.