Wheaton, Ann. Centers for Disease Control and Prevention, August 6, 2015. Fewer than 1 in 5 middle and high schools in the U.S. began the school day at the recommended 8:30 AM start time or later during the 2011-2012 school year, according to data published today in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report. Too-early start times can keep students from getting the sleep they need for health, safety, and academic success.