Vermont's legislature attempted to pass a law to this effect in this past session, bu t it died in committee after our health commissioner, of all people, went public with his skepticism. (We are pouring state tax dollars into lawsuits against social media companies for exploiting children - interesting that school boards in Ontario are doing this as well - but can't take the most minimal step to protect classrooms, apparently.) There are a few other US states considering similar laws (e.g. Ohio). It's an outrageous symptom of social decay that teachers and principals can't do this of their own accord in so many places.
