When Seattle’s new school superintendent, Ben Shuldiner, was making the rounds last fall before being officially hired, he frequently spoke about areas of “low-hanging fruit” in the district — quick changes that would have impact right out of the gate. On Monday, three months into the job, Shuldiner made good by doing something his predecessors should have years ago: implementing a “bell to bell” ban on cellphones in all elementary and middle schools, with a looser version for high schools that allows students to use their phones during lunch and passing periods. That relaxed standard for older students fails to address the powerfully addictive effect of these devices, and it is disappointing. (Physicians believe millions of kids may have “ media use disorder .”) But it is also realistic, since most high school campuses are open during lunch, when it would be impossible to police students’ phone use.…