Teenagers need eight to ten hours of sleep per night. However, in adolescence (青春期) changes to the body's sleep cycle make it difficult for teens to fall asleep early. Many cannot fall asleep until 10:30 p.m. or even later and most of them will feel sleepy if they have to get up too early.

 Scientists recommend that both middle and high schools begin no earlier than 8:30 a.m. Later school start times support the natural needs of teenagers and increase their sleeping time. 

 Here are some other benefits of later school start times: 

 More time for a healthy breakfast 

 When running late in the mornings, students are likely to go without breakfast. With an empty stomach, one finds it difficult to focus (集中) in class. When they are always in a hurry, students may form unhealthy eating habits. 

 With extra time before going to school, students can eat a well-balanced breakfast and focus more on learning. 

 Fewer behavioral (行为的) problems 

 Teens experience mood changes as a common result of this special period of life. Less sleep may cause worries, stress and unhappiness. 

When they get enough sleep, students are calm and peaceful and their moods do not change suddenly. They're less likely to feel worried, unhappy or get angry. For parents, children with more sleep are easier to live with.

 Better performance (表现) in study 

 Sleep loss hurts attention, memory and brain development. Students with less sleep have difficulty paying attention in class and are likely to have lower grades. Students with enough sleep can be more energetic during the day and more willing to learn. They are also less likely to fall asleep in class and more able to understand what they learn. 

In conclusion, starting school later helps students get a better night's sleep. It improves their chances of eating, behaving and performing better.