Đáp án cho [Recent Tests- VOL] - Starting school late

Starting school later has positive effects on teens

A growing body of evidence demonstrates that descents benefit from more sleep.

When school districts push back the start of the school day, good things happen.

1-2With classes that start as early as 7 am and buses that pull up long before sunrise some 80% of US children in grades 6 through 12 are not getting the recommended amount of sleep during the school year,2 according to research by the National Sleep Foundation, a sleep advocacy group. These early start times contribute to a myriad of problems. Exhausted children, studies suggest, not only struggle with mutability, but also with depression. They gain weight and their grades suffer, and many turn to caffeine, with questionable results for productivity and unknown effects on the development of young brains.

Now, fueled by accumulating research designed to sleep late and that delaying school start times even by just 30 minutes makes a huge difference in how well teens feel and perform, an increasing number of schools around the United States are starting the school day later than they used to. Many more are thinking about it. 3At the same time, however, there are strong pockets of resistance to change from administrators and parents who think that bus schedules will get too complicated, that starting later will interfere with after-school programs or that children will simply stay up later if they know they can sleep in a little more.

4According to Kyla Wahistrom, director of the Center for Applied Research and Educational Improvement at the University of Minnesota, even though the two districts could not be more different in terms of race, socioeconomics and other factors, changes in both places appeared immediately.

5Some of the outcomes were quite significant. For instance, students were noticeably more alert in the first two periods of the day. In addition, the cafeteria was calmer, and there were fewer fights in the halls. Students, who were now getting nearly an hour more sleep each night, said they felt less depressed. Even parents told teachers they thought their kids were easier to live with.

The melatonin shift

Blame biology, not laziness, for making teens reluctant to get up in the morning. 6-7As children grow older and approach puberty, a period of important biological change, their bodies circulate melatonin, the hormone that brings on sleepiness, two hours later than before.

As a result, teens find it impossible to fall asleep until about 11 p.m., even if they try to go to bed earlier. Yet teenagers still need an average of 9.25 hours of slumber each night. On top of the shift in natural sleeping and waking times, there is also another factor. 8This is related to a period of intense sleepiness which hits both adults and adolescents during the early morning hours. In adults this low point in alertness hits between 3 a.m. and 5 a.m.; in adolescents, it falls between about 5 a.m. and 7 a.m.. That means that, while their alarm clocks are telling teens to get out of bed and demand that their brains perform, their bodies signal to them to keep sleeping.

In addition to the mood behavior and learning issues, scientists are starting to uncover more subtle ways in which such chronic lack of sleep can hurt children. Some studies, for example, show that sleep deprivation compromises the immune system. 9Others suggest that, with too little sleep, the body releases higher levels of hormones that induce hunger, possibly contributing to growing rates of obesity.

To stay awake, young people often turn to coffee, soda and other caffeinated beverages. In a public high school in the eastern US state of Massachusetts, 1095% of polled students reported drinking caffeine in the prior two weeks, mostly in the form of soda as opposed to coffee and most often in the afternoon and evening hours, Dr Amy Wolfson and a colleague reported in Health Education and Behavior. According to Dr Wolfson, there are no published guidelines for how much caffeine is too much for adolescents. 11However, the substance stays in the body for up to five hours, which is three hours longer than originally thought, and is costing teens unknown hours of sleep. 12Even if caffeinated teens manage to fall asleep, caffeine worsens the quality of their sleep. 13Finally, no one knows how caffeine might affect developing brains, although plenty of experts are concerned about the link between sugar in soda and weight gain.

Schools respond

As the sleep research piles up, a growing number of schools are moving toward later start times. No one has kept track of how many schools have made the change, but experts say they are fielding a growing number of calls from districts around the US asking for advice about whether and how to switch to later start times. Whatever it takes, teenagers need to get enough sleep. Changing school start times has proven to be one way to achieve this.