Reading passage
Sleep is not simply a period of rest for the human body; it is an active process during which the brain sorts memories, repairs damaged tissues and releases important hormones. For teenagers, this process is especially critical because their bodies and brains are still developing. Yet surveys in many countries show that the majority of secondary school students sleep far less than the nine hours per night that specialists recommend. The average teenager in large cities now sleeps only about seven hours on school nights, and many manage considerably less than that during busy exam periods.
One important reason for this shortage is biological. During puberty, the internal body clock of adolescents shifts naturally, so that they feel sleepy later at night and want to wake later in the morning. The hormone melatonin, which makes people feel tired, is released about two hours later in teenagers than in younger children or adults. As a result, a sixteen-year-old may not feel sleepy until eleven at night, even when parents insist on an early bedtime. This is not laziness or bad behaviour; it is a normal part of growing up that affects almost every teenager in the world.
This natural shift, however, clashes with the timetable of most schools. In many countries, secondary schools begin between seven thirty and eight in the morning, and some start even earlier. When teenagers must rise at six o'clock to travel to school, their body clock still behaves as if it were the middle of the night. Researchers describe this state as social jet lag, because students experience the same symptoms as travellers who have crossed several time zones: tiredness, poor concentration and a constant desire to return to bed.
Technology adds a second pressure on top of biology. Mobile phones and computers emit blue light, which tells the brain that it is still daytime and delays the release of melatonin even further. A survey in one European country found that more than sixty percent of fifteen-year-olds used a mobile phone in bed every night, and those who did so fell asleep on average forty minutes later than classmates who kept their devices outside the bedroom. Late-night messages and videos also keep the mind active at the very moment it should be calming down.
The consequences of sleep loss are serious and wide-ranging. Teachers report that tired pupils struggle to concentrate in morning lessons, and laboratory studies confirm that lack of sleep weakens attention and short-term memory. Sleep-deprived teenagers also show stronger emotional reactions: small problems can produce anger or anxiety that would never occur after a full night of rest. Furthermore, several long-term studies link poor sleep in adolescence to weight gain, weaker immune systems and a higher risk of depression in early adult life.
In response to these findings, some school districts in the United States have moved their starting time later. One large district in the state of Minnesota changed its first lesson from 7:25 to 8:30 in the morning, and researchers followed the results carefully. After the change, attendance improved, the number of car accidents involving teenage drivers fell, and students reported feeling less tired during the school day. Average grades rose slightly, particularly in subjects taught during the first two lessons of the morning.
Not everyone agrees with such reforms. Opponents argue that later start times create practical problems for families, because parents may leave for work before their children go to school. Sports coaches worry that training sessions would finish after dark in winter, and bus companies point out that new timetables would raise transport costs considerably. These concerns help to explain why change has been slow, and why most schools around the world still begin their teaching day before eight thirty in the morning.
Sleep experts, nevertheless, offer practical advice that does not require a new timetable. They suggest that teenagers keep a regular bedtime, even at weekends, and stop using screens at least one hour before sleeping. Morning sunlight also helps to reset the body clock, so walking to school rather than taking a bus can bring small but real benefits. None of these steps is difficult or expensive, but together they can add a valuable extra hour of rest to the life of a busy and tired teenager.