More than 1 in 4 of the nation’s full-time teachers are considered chronically absent from school, according to federal data, missing the equivalent of more than two weeks of classes each academic year in what some districts say has become an educational crisis. The U.S. Education Department’s Office for Civil Rights estimated this summer that 27 percent of the nation’s teachers are out of school for more than 10 days of regular classes — some missing far more than 10 days — based on self-reported numbers from the nation’s school districts. But some school systems, especially those in poor, rural...