In her new book, “The Smartest Kids in the World,” Amanda Ripley, an investigative journalist, tells the story of Tom, a high-school student from Gettysburg, Pennsylvania, who decides to spend his senior year in Warsaw, Poland. Poland is a surprising educational success story: in the past decade, the country raised students' test scores from significantly below average to well above it. Polish kids have now outscored(超过……分数) American kids in math and science, even though Poland spends, on average, less than half as much per student as the United States does. One of the most striking differences between the high school Tom attended in Gettysburg and the one he ends up at in Warsaw is that the latter has no football team, or, for that matter, teams of any kind.

    That American high schools waste more time and money on sports than on math is an old complaint. This is not a matter of how any given student who plays sports does in school, but of the culture and its priorities. This December, when the latest Program for International Student Assessment (PISA) results are announced, it's safe to predict that American high-school students will once again display their limited skills in math and reading, outscored not just by students in Poland but also by students in places like South Korea, Belgium, the Netherlands, Finland, Singapore, and Japan. Meanwhile, they will have played some very exciting football games, which will have been breathlessly written up in their hometown papers.

    Why does this situation continue? Well, for one thing, kids like it. And for another, according to Ripley, parents seem to like the arrangement, too. She describes a tour she took of a school in Washington D.C., which costs thirty thousand dollars a year. The tour leader—a mother with three children in the school—was asked about the school's flaws(瑕疵). When she said that the math program was weak, none of the parents taking the tour reacted. When she said that the football program was weak, the parents suddenly became concerned. “Really?” one of them asked worriedly, “What do you mean?”

    One of the ironies(讽刺) of the situation is that sports reveal what is possible. American kids' performance on the field shows just how well they can do when expectations are high. It's too bad that their test scores show the same thing.

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    Bad news sells. If it bleeds, it leads. No news is good news, and good news is no news. Those are the classic rules for the evening broadcasts and the morning papers. But now that information is being spread and monitored(监控) in different ways, researchers are discovering new rules. By tracking people's e-mails and online posts, scientists have found that good news can spread faster and farther than disasters and sob stories.

    “The 'if it bleeds' rule works for mass media,” says Jonah Berger, a scholar at the University of Pennsylvania. “They want your eyeballs and don't care how you're feeling. But when you share a story with your friends, you care a lot more how they react. You don't want them to think of you as a Debbie Downer.”

    Researchers analyzing word-of-mouth communication—e-mails, Web posts and reviews, face-to-face conversations—found that it tended to be more positive than negative, but that didn't necessarily mean people preferred positive news. Was positive news shared more often simply because people experienced more good things than bad things? To test for that possibility, Dr. Berger looked at how people spread a particular set of news stories: thousands of articles on The New York Times' website. He and a Penn colleague analyzed the “most e-mailed” list for six months. One of his first findings was that articles in the science section were much more likely to make the list than non-science articles. He found that science amazed Times' readers and made them want to share this positive feeling with others.

    Readers also tended to share articles that were exciting or funny, or that inspired negative feelings like anger or anxiety, but not articles that left them merely sad. They needed to be aroused(激发) one way or the other, and they preferred good news to bad. The more positive an article, the more likely it was to be shared, as Dr. Berger explains in his new book, “Contagious: Why Things Catch On.”

    One night about nine o'clock, Dr. Eyck, a surgeon, had a phone call from Dr. Haydon at the hospital in Clens Falls. The surgeon was asked to go there at once to operate on a very sick boy who shot himself while playing with a gun.

    The doctor was soon on his way to Clens Falls. It was 60 miles away. And it was snowing heavily in the city. The surgeon thought he could get there before 12 o'clock.

    A few minutes later, the doctor was stopped by a man in an old black coat. Gun in hand, the man ordered the doctor to get out. Then the man drove the car down the road, leaving the doctor in the falling snow.

    It was after 2 o'clock in the morning when the doctor arrived at the hospital in Clens Falls. Dr. Haydon told him that the boy had died an hour before.

    The two doctors walked by the door of the hospital waiting room. There sat the man in the old black coat with his head in his hands.

    "Mr. Cuninghan," said Dr. Haydon to the man, "This is Dr. Eyck. He is the surgeon who walked all the way from Albany to save your boy."

    Your kids learn a lot from their friends—things you can't teach them, no matter how much you want to.

    Probably the most important thing kids learn is how to have peer relationships. As a parent, you can't do this, because you and your child aren't equals.

    For example, when you're sitting on your family room floor and your very young child asks you to pass him the blocks, you probably hand them right over. If your child is sitting with a peer and asks the same thing, though, he might not get what he wants.

    To succeed, your child will need to learn strategies for getting what he wants. For example, he might simply yank (猛拉) the toy out of his friend's hand. If he does that, he may learn that it's not the best way of getting what he wants because it leads to fighting and time­outs. The successful child will learn that he needs to negotiate a trade, to wait patiently, or to find something else equally fun to play with.

    Friends also provide emotional support, something that is part of the foundation of healthy adulthood. You can't be with your child on the elementary school playground or at the high school dance. Your child's friends will be the ones to stick up for her, to include her in games, and later, to tell her she looks great even if her lousy prom (糟糕的舞会) date wanders off instead of dancing with her.

    Friends also help your children learn. Friends solve problems together, imitate each other, and pass on knowledge.

    Some experts believe that the single biggest predictor of your child's success later in life is her ability to make friends. In fact, they claim it's even more important than IQ and grades.

    This doesn't mean that the kids who are most popular in school do the best later on in life. What matters is not the number of friends a child has but rather the quality of the relationships.

    This is good news for those of us who hate to think that popularity really is the Holy Grail of childhood and adolescence. While it's true that popularity has many advantages, and that many popular kids really are nice people—and not just the best dressed or best looking—it's better to have a few good friends than to have the admiration of the masses.

    People have grown taller over the last century, with South Korean women shooting up by more than 20cm on average, and Iranian men gaining 16.5cm. A global study looked at the average height of 18-year-olds in 200 countries 1914 and 2014. The results show that while Swedes were the tallest people in the world in 1914, Dutch men have risen from l2th place to claim top spot with an average height of 182.5cm. Larvian women, meanwhile, rose from 28th place in 1914 to become the tallest in the world a century later, with an average height of 169.8cm. James Bentham, a co-author of the research says the global trend is likely but once you average over whole populations, genetics plays a less key role," he added.

    But while height has increased around the world, the trend in many countries of north and sub-Saharan Africa causes concern, says Elio Riboli of Imperial College. While height increased in Uganda and Niger during the early 20th century, the trend has reversed in recent years, with height decreasing among 18-year-olds.

    "One reason for these decreases in height is the economic situation in the 1980s," said Professor Alexander. The nutritional and health problems that followed the policy of structural adjustment, he says, led to many children and teenagers failing to reach their full potential in terms of height.

    Bentham believes the global trend of increasing height has important implications. "How tall we are now is strongly influenced by the environment we grew up in," he said. "If we give children the best possible start in life now, they will be healthier and more productive for decades to come."