Schools across Britain are being asked to take part in a research project known as Teensleep to stagger (错开) their start times to suit the different biological clocks of children, with 10-year-olds starting at 9 am and 15-year-olds starting at 10 am. Scientists believe that the body’s circadian rhythm (生理节律), which determines sleep-wake patterns over 24-hour periods, varies with a child’s age and that an earlier school start time for all students is not in the best interests of older children. “The research project will sign up 100 schools as part of the biggest study yet into the role that school start times play in the health of students,” said Paul Kelley of the University of Oxford.

“The natural change in the biological clock to later in the 24-hour cycle is particularly obvious in the 14 to 24 age group. The change in the biological clock continues in later middle age, when people usually go back to the naturally earlier start time they felt comfortable with when they were 10-year-old children,” Dr Kelley said.

“By the time you are 18, 19 or 20 you are suffering on average two hours of sleep loss a day and that is increasing so that at the end of the week you have suffered 10 hours of sleep loss. It has a hugely damaging impact on the body,” Dr Kelley told the Seience Festival in Bradford.

“Students lose more sleep than doctors working a 24-hour shift during every school or university week... Schools are starting at any time they choose. There is no justification and no study suggesting that starting earlier is better,” he said. “Most people wake up to alarms because they don’t naturally wake up at the time they go to work, so we are a sleep-deprived (睡眠不足) society and this age group, 14 to 24, is more deprived than any other group of society,” he added.

Most students have biology classes in the classrooms or the labs in China．But several days ago，I had a biology class outside in my American school．

My biology teacher，Mr. Kwak，divided us into three groups and asked us to play a game about natural selection(自然选择) and how birds find food．

He gave the first group one spoon per person，the second group forks and my group knives．I thought we were going hunting，so knives might work better．Surprisingly，he told us to pick up the beans on the grass with our tools．

When the game started, all of us ran to the grass area.We squatted(蹲)down and looked for beans. It was hard to pick up something that small，especially from the grass .

When I almost lifted a bean，it dropped back to the ground.When I finally picked up several beans, one of my friends ran into me．I couldn’t keep my balance and fell over．All my beans dropped to the ground! Just at that moment，Mr. Kwak called us back．I had to leave the game and of course I got a bad result．I couldn’t help thinking that if I were a bird living on Galapagos Island，I would be dead soon．

The fun game made me realize that natural selection is really competitive(竞争的)．Everyone is trying his or her best to survive．

Holidays are really important. Many of us will have childhood memories of summer holidays where we were taken away from home to experience new environments and learn in different ways.

But holidays are expensive and, for those on low wages or living on benefits, they are often unobtainable. Even the cheapest holidays require travel and other additional costs that are difficult for many families to meet.

For working parents，the long summer break can be a very difficult problem for childcare. When an annual leave allowance amounts to only five weeks，there is a need to spread this across the year. Couples can find themselves taking leave in turn in order to care for children who are on holiday. For some，this makes even an affordable family holiday difficult.

The schools that I visit in Nottingham are full of experienced staff committed to giving our children a caring and inspiring learning environment. The number of children receiving free school meals is quite large in Nottingham and many schools have breakfast clubs to make sure that children get a healthy start to the day. Most schools undertake programs of group or individual educational support. Schools also have an important role in safeguarding children’s welfare through the ongoing touch and support with their pupils. During the long summer holidays，much of this is missed.

While teachers are holidaying in the UK, many of their pupils spend the whole six weeks on the street where they live. The lack of free school meals for six weeks can result in pressure on a family budget and an inability to afford the inspiring experiences that help children to continue their learning.

In setting out its plans for a five-term year, Nottingham City Council (委员会）is seeking to reduce the summer holiday down to four and a half weeks, with a more balanced five terms of roughly eight weeks, each followed by a two-week break. We believe this will give real “down time" for school staff and pupils alike but will be short enough not to cause a real break in learning.

We acknowledge that this change may be difficult for some school staff, particularly whose own children are educated in other authorities. However, this must be weighed against the benefits for city children for whom we all have the greatest duty of care.