Banning phones in schools has emerged as a rare bipartisan policy across America. As the school year begins, millions of students in 17 states, from New York to Kentucky, will be newly prohibited from taking phones into the classroom, bringing the total to 35 states with such laws or rules. America is no outlier here. Around the world bans on phones are being enacted or proposed in at least 40% of national education systems, with the aim of helping students focus. But whereas political momentum for keeping classrooms phone-free is growing, researchers have noted that scientific evidence for the benefits is thin: a few small-scale studies with differing designs yielded mixed results.