Numerous studies have concluded that the later start times are healthier for kids, reduce juvenile crime, improve grades, boost sports performance and even result in better teenage driving records, because sleepy teens cause more accidents. Between 1,000-2,000 individual school districts across the United States recently moved high school start times to approximately 8:30 a.m., the earliest start time recommended by the American Medical Association. But such changes come with difficult ripple effects — upended bus schedules, later starts for extracurriculars and new schedules for teachers and staff — making many other states and localities hesitant to change.