>For the past few years, parents, researchers, and the news media have paid closer attention to the relationship between teenagers’ phone use and their mental health. Researchers such as Jonathan Haidt and Jean Twenge have shown that various measures of student well-being began a sharp decline around 2012 throughout the West, just as smartphones and social media emerged as the attentional centerpiece of teenage life. Some have even suggested that smartphone use is so corrosive, it’s systematically reducing student achievement.