Because it is tough for high school students to fall asleep early enough. "In the teenage years, the hormonal response to the 24-hour daily light/dark exposure

Because it is tough for high school students to fall asleep early enough. "In the teenage years, the hormonal response to the 24-hour daily light/dark exposure that influences circadian rhythm is altered, making adolescents physiologically yearn to stay awake later at night and to remain asleep later in the day." https://www.neurologytimes.com/blog/teenage-circadian-rhythm https://www.neurologytimes.com/blog/teenage-circadian-rhythm