Cellphones have become a school scourge. More than 70% of high school teachers say student phone distraction is a “major problem,” according to a survey this year by Pew Research. That’s why states are mounting a bipartisan effort to crack down on rampant student cellphone use. So far this year, at least eight states have passed laws, issued orders or adopted rules to curb phone use among students during school hours. The issue isn’t simply that some children and teenagers compulsively use apps