A lack of confidence isn’t what’s holding back working women.

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.