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The change can be baffling to many parents: Their young girls are masters of the universe, full of gutsy fire. But as puberty sets in, their confidence nose-dives, and those same daughters can transform into unrecognizably timid, cautious, risk-averse versions of their former self.

Over the course of writing our latest book, we spoke with hundreds of tween and teen girls who detailed a striking number of things they don’t feel confident about: “making new friends,” “the way I dress,” “speaking in a group.” In our research, we worked with Ypulse, a polling firm that focuses on tweens and teens, to survey more than 1,300 girls from the ages of 8 to 18 and their parents. (The sample was broadly representative of the country’s teen population in terms of race and geographic distribution.) The data is more dramatic than we’d imagined: The girls surveyed were asked to rate their confidence on a scale of 0 to 10, and from the ages of 8 to 14, the average of girls’ responses fell from approximately 8.5 to 6—a drop-off of 30 percent.

Until the age of 12, there was virtually no difference in confidence between boys and girls. But, because of the drop-off girls experienced during puberty, by the age of 14 the average girl was far less confident than the average boy. Many boys, the survey suggested, do experience some hits to their confidence entering their teens, but nothing like what girls experience. (The Ypulse survey did not break down its findings at a granular enough level to discern if there was any correlation between kids’ race or income level and their self-described confidence.)

The female tween and early-teen confidence plunge is especially striking because multiple measures suggest that girls in middle and high school are, generally speaking, outperforming boys academically, and many people mistake their success for confidence. But the girls we talked with and polled detailed, instead, a worrisome shift. From girls 12 and under, we heard things such as “I make friends really easily—I can go up to anyone and start a conversation” and “I love writing poetry and I don’t care if anyone else thinks it’s good or bad.” A year or more into their teens, it was “I feel like everybody is so smart and pretty and I’m just this ugly girl without friends,” and “I feel that if I acted like my true self that no one would like me.”

Confidence is an essential ingredient for turning thoughts into action, wishes into reality. Moreover, when deployed, confidence can perpetuate and multiply itself. As boys and girls (and men and women) take risks and see the payoffs, they gain the courage to take more risks in the future. Conversely, confidence’s absence can inhibit the very sorts of behaviors—risk taking, failure, and perseverance—that build it back up. So the cratering of confidence in girls is especially troubling because of long-term implications. It can mean that risks are avoided again and again, and confidence isn’t being stockpiled for the future. And indeed, the confidence gender gap that opens at puberty often remains throughout adulthood.

What makes confidence building so much more elusive for so many tween and teen girls? A few things stand out. The habit of what psychologists call rumination—essentially, dwelling extensively on negative feelings—is more prevalent in women than in men, and often starts at puberty. This can make girls more cautious, and less inclined toward risk taking. Additionally, at an early age, parents and teachers frequently encourage and reward girls’ people-pleasing, perfectionistic behavior, without understanding the consequences. Often, this is because it just makes parents’ and teachers’ lives easier: In a busy household or noisy classroom, who doesn’t want kids who color within the lines, follow directions, and don’t cause problems? But perfectionism, of course, inhibits risk taking, a willingness to fail, and valuable psychological growth. “If life were one long grade school,” Carol Dweck, the Stanford University psychologist who wrote The Growth Mindset, explained to us in an interview for our first book, women “would be the undisputed rulers of the world. But life isn’t one long grade school.”

In fact, later in life, the goalposts shift considerably. “It rewards people who take risks and rebound,” Dweck added. And the boys in our survey seemed to have a greater appetite for risk taking: Our poll shows that from ages 8 to 14 boys are more likely than girls to describe themselves as confident, strong, adventurous, and fearless.

Teen and tween girls are focused instead, according to our polling data, on setting impossibly high standards for themselves: Our polling data shows that the proportion of girls who say they are not allowed to fail rises from 18 to 45 percent from the ages of 12 to 13. In their efforts to please everyone, achieve more, and follow rules, many girls are actually nurturing traits in themselves that set them up to struggle in the long run. Adding to this, many girls are also wise enough by the age of 12 to see that the world still treats men and women differently—that dings their confidence, too.

Social media doesn’t help either, and its ill effects might hit girls harder than boys. The internet can multiply social stresses astronomically. In the past, girls could have an overwhelming day at school, fight with a friend, and get a “bad” grade, but go home and get some distance. There’s no distance anymore—only constant, instant, and public condemnation or praise.

There’s evidence that tweaking the status quo, and acclimating girls at this critical age to more risk taking and failure, makes a difference. Some of the most compelling data links participation in sports to professional success. A study from the accounting firm EY and espnW, ESPN’s women’s site, found that 94 percent of the women currently with C-suite jobs in the U.S. played competitive sports. It’s not only through athletics that young girls can gain confidence; sport is simply an organized and easily available opportunity to experience loss, failure, and resilience. But the same skills can be acquired by participating on a debate team, learning to cook, or speaking up on behalf of a cause like animal welfare—as long as there is a move outside of her comfort zone, and a process of struggle and mastery, confidence will usually be the result.

It’s essential to close the gap, and to do so early, because the long-term effects of these dynamics hurt not only girls, but the women they become, many of whom, within a few years of entering the workforce, experience another confidence drop, and a drop in aspirations. Their rule-following, good-girl methods have been celebrated, rewarded by a structured educational and societal system. It’s a shock to arrive in the adult world and discover a dramatically new playing field: Failure is okay. Risk is worth it. No wonder they struggle: Their whole life, to date, they’ve internalized just the opposite, a societal bait and switch that should be recognized. Girls are adept at learning—they just need the right study guide.

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