The early weeks of a school year can rattle even the most self-assured kid — the swirl of new classes, teachers and tribes, and the pressure to try out new extracurriculars, sports and even personalities.

Tween and teen girls face an added challenge because their confidence is already plummeting during those years. Of course, puberty is a turbulent time for confidence in both genders. But girls experience a much more significant, dramatic drop.

For our book, “The Confidence Code for Girls,” we worked with Ypulse, a polling firm that focuses on tweens and teens, to survey more than 1,300 girls from ages 8 to 18 and their parents. Between the ages of 8 and 14, girls’ confidence levels fall by 30 percent. At 14, when girls are hitting their low, boys’ confidence is still 27 percent higher. And the effects can be long lasting.

So how can you spot the signs of this confidence plunge in your daughter? She may grow more unwilling to take risks, to try something new, to fail. It might be a reluctance to speak up in class, to try out for a new sport or put herself out there with an unfamiliar classmate. Overthinking, people-pleasing and perfectionism typically kick in, effectively grinding her confidence to a halt.