Cell phones are still absent from most U.S. schools, but recent data is now showing they are steadily gaining acceptance. This can be seen as administrators bow to parents’ wishes to keep tabs on their kids, and teachers finding ways to work them into lessons. The percentage of K-12 public schools that prohibited cell phone use was about 66 percent in 2015-16, down from more than 90 percent in 2009-10, according to data from a survey conducted by the National Center for Education Statistics. Among high schools, the shift over the same period was especially striking — dropping from 80 percent with bans to 35 percent.