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It is 7:15 on a Sunday morning in Jerusalem, and Noam, sixteen, is trying to wake up. He went to bed after midnight, and his first lesson starts at eight. "My parents say I'm lazy," he says. "But I just can't fall asleep early." Scientists say that Noam is probably telling the truth.

Sleep experts say that teenagers need between eight and ten hours of sleep a night. That is more than most adults need. However, many teenagers sleep much less. In the United States, studies found that about seven out of ten high school students sleep less than eight hours on school nights.

Part of the reason is biology. Everyone has a body clock that tells us when to feel awake and when to feel tired. In the evening, the brain produces a hormone called melatonin, which makes us sleepy. During puberty, the body clock moves later: the brain starts producing melatonin later in the evening. As a result, many teenagers do not feel tired until eleven at night or later. Since school starts early, they simply do not get enough hours of sleep.

Why does this matter? While we sleep, the brain is busy. It stores the things we learned during the day, so sleep is important for memory. Teenagers who do not sleep enough find it harder to concentrate, and they are often in a bad mood. Tired drivers are also more likely to have accidents, because they react more slowly.

Teenagers cannot change their body clock, but they can help it. Experts advise going to bed and getting up at about the same time every day, even on weekends. Bright light from screens in the evening can make it harder to fall asleep, so it is a good idea to put the phone away before bed. Caffeine can stay in the body for many hours, so a cup of coffee at nine at night is not a good idea either. Noam now leaves his phone in the kitchen at night. "I still don't love Sunday mornings," he says, "but I'm not a zombie any more."

It is 7:15 on a Sunday morning in Jerusalem, and Noam, sixteen, is trying to wake up. He went to bed after midnight, and his first lesson starts at eight. "My parents say I'm lazy," he says. "But I just can't fall asleep early." Scientists say that Noam is probably telling the truth.

Sleep experts say that teenagers need between eight and ten hours of sleep a night. That is more than most adults need. However, many teenagers sleep much less. In the United States, studies found that about seven out of ten high school students sleep less than eight hours on school nights.

Part of the reason is biology. Everyone has a body clock that tells us when to feel awake and when to feel tired. In the evening, the brain produces a hormone called melatonin, which makes us sleepy. During puberty, the body clock moves later: the brain starts producing melatonin later in the evening. As a result, many teenagers do not feel tired until eleven at night or later. Since school starts early, they simply do not get enough hours of sleep.

Why does this matter? While we sleep, the brain is busy. It stores the things we learned during the day, so sleep is important for memory. Teenagers who do not sleep enough find it harder to concentrate, and they are often in a bad mood. Tired drivers are also more likely to have accidents, because they react more slowly.

Teenagers cannot change their body clock, but they can help it. Experts advise going to bed and getting up at about the same time every day, even on weekends. Bright light from screens in the evening can make it harder to fall asleep, so it is a good idea to put the phone away before bed. Caffeine can stay in the body for many hours, so a cup of coffee at nine at night is not a good idea either. Noam now leaves his phone in the kitchen at night. "I still don't love Sunday mornings," he says, "but I'm not a zombie any more."

It is 7:15 on a Sunday morning in Jerusalem, and Noam, sixteen, is trying to wake up. He went to bed after midnight, and his first lesson starts at eight. "My parents say I'm lazy," he says. "But I just can't fall asleep early." Scientists say that Noam is probably telling the truth.

Sleep experts say that teenagers need between eight and ten hours of sleep a night. That is more than most adults need. However, many teenagers sleep much less. In the United States, studies found that about seven out of ten high school students sleep less than eight hours on school nights.

Part of the reason is biology. Everyone has a body clock that tells us when to feel awake and when to feel tired. In the evening, the brain produces a hormone called melatonin, which makes us sleepy. During puberty, the body clock moves later: the brain starts producing melatonin later in the evening. As a result, many teenagers do not feel tired until eleven at night or later. Since school starts early, they simply do not get enough hours of sleep.

Why does this matter? While we sleep, the brain is busy. It stores the things we learned during the day, so sleep is important for memory. Teenagers who do not sleep enough find it harder to concentrate, and they are often in a bad mood. Tired drivers are also more likely to have accidents, because they react more slowly.

Teenagers cannot change their body clock, but they can help it. Experts advise going to bed and getting up at about the same time every day, even on weekends. Bright light from screens in the evening can make it harder to fall asleep, so it is a good idea to put the phone away before bed. Caffeine can stay in the body for many hours, so a cup of coffee at nine at night is not a good idea either. Noam now leaves his phone in the kitchen at night. "I still don't love Sunday mornings," he says, "but I'm not a zombie any more."