It is no secret that physical activity is necessary to a person’s well­being.Because children are continuously developing physically and emotionally，they are especially affected by the benefits of activity.Former First Lady Michelle Obama’s initiative “Let’s Move！” reports that nearly one­third of US children are overweight or obese，and that “schools are a key setting for kids to get their 60 minutes of play with moderate activity，given the significant portion(部分) of time they spend there.”

Physical education programs in schools directly benefit students’ physical health.Regular exercise promotes muscles and bone development.In addition to participating in physical activity，students in P. E.learn the fundamentals of a healthful lifestyle，the building blocks upon which they can develop into healthy，knowledgeable adults.

Though the lack of attention on P. E.is often justified as an opportunity to spend more time in the classroom，studies show that physical activity contributes to improved academic performance.Regular activity during the school day is strongly associated with higher concentration levels.A statewide policy in North Carolina requires that children from kindergarten to eighth grade participate in 30 minutes of physical activity each day.

Activities in P. E.help children develop healthful social interactions.From a young age，children learn cooperation through group activities and form a positive sense of identity as part of a team.Such group activities are continually important as children grow older.The International Platform on Sport and Development states that sport has been used as a practical tool to engage young people in their communities through volunteering，resulting in higher levels of leadership and community engagement among young people.

The benefits of P. E.to a child’s mental health are both complex and comprehensive.Improved physical health，academics and social interactions all contribute to good mental health.Physical activity sets the stage for a good night’s sleep，provides more energy to participate in hobbies and interact with others.

A typical school day in the UK starts around 8:30 am. This is often even earlier elsewhere in the world, with students sitting down to their first lesson at 7:30 am in the US. According to studies about sleep, the average teenager needs eight to nine hours’ sleep each night, but in fact a lot of teenagers struggle to get this much. A lot of problems happen because our sleep patterns are not fixed and they change as we grow.

So, a later school start time could help to solve this problem, by making sure teenagers can get eight plus hours of sleep and react properly to body’s natural rhythms (规律). There has been a general change over the past 25 years to shorten the school day. This is not at the cost of teaching time but at the cost of natural breaks, which has led to reduced lunch time and lesson breaks.

Actually, later start times could help teens’ grades and health. This is mainly because it makes the management of children easier. Managing hundreds of children “playing” requires effective staffing. And there is always the fear that behavior worsens during breaks. So the theory (理论) goes that having children in class and strictly supervised must be better. But this means that students seldom have enough time to absorb (吸收) what they were doing in maths before suddenly they are forced to study ancient history. And teaching staff also move through from one class to another, with hardly a rest or time to refocus.

Professor Wilson from Yale University has studied sleep patterns for almost ten years. He said that the later start time of the school day could benefit everyone included. Anyway, it could also lead to better achievement in teenagers and less of a struggle for parents in the mornings. For teachers, it could also mean a less stressful day all around and what could be better than that?