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What's Normal for Teen development

Biological and Physical Changes

This fact sheet is part of the Teen talk: A survival guide for parents of teenagers series.

Colleen Gengler, Extension Educator, emerita — Family Relations

2011. Reviewed February 2017 by Jodi Dworkin, Extension Specialist and Associate Professor — Family Social Science.

young girls

Teens experience rapidly changing bodies that can as much as double in size while they also develop more adult-like physical features. They are also becoming sexually mature, which includes physical changes as well as new feelings about their bodies, sexuality, and intimate relationships.

Physical Changes

Puberty occurs at widely varying ages. For girls, puberty can begin as early as 8 years of age but more commonly starts about age 10. Girls may experience a growth spurt in height and overall body shape in the early teen years. Girls will continue to grow, although a little more slowly, until age 17 or 18. They will begin to develop breast buds as early as 8 years of age, reaching full breast development anywhere from 12 to 18 years. Pubic hair growth as well as armpit and leg hair can begin at around age 9 or 10. Menarche, the beginning of menstrual periods, usually begins about two years following the first signs of puberty. That may be as early as age 10 and as late as age 15 with the average in the U.S. at about age 12.5.

Boys begin their growth spurt in height at age 10 or 11, peaking at around age 14, and finish growing physically at about age 21. The genitals begin to enlarge as early as 9 years of age with adult size and shape achieved at about age 16 or 17. Boys' voices experience changes at about the same time.

Early or Late Development

Early and late maturation has different implications for girls and for boys. With girls already ahead of their male peers, girls who begin maturing early may be out of sync with both male and female peers. Physical maturation can occur before maturing mentally, socially, and emotionally. Girls' concerns might include:

This can result in having to cope with situations beyond their emotional and cognitive abilities.

For boys, concerns may be more about delayed development. Typically, boys are already behind physically as compared to their female classmates and if there is delayed development, the differences become more apparent. Teasing or bullying can occur resulting in low self-esteem or even depression.

What Parents Can Do

Getting used to a rapidly changing body can result in teens feeling uncomfortable with who they are becoming and what they look like. They might also experience physical awkwardness when one part of the body hasn't caught up with the rest. Here’s what you as a parent can do.


McNeely, C., & Blanchard, J. (2010). The teen years explained: A guide to healthy adolescent development. Baltimore: Center for Adolescent Health, Johns Hopkins Bloomberg School of Public Health.

Simpson, A. R. (2001). Raising teens: A synthesis of research and a foundation for action. Boston: Center for Health Communication, Harvard School of Public Health.

Steinberg, L. (2008). Adolescence. New York: McGraw-Hill.

Related resources

Social and Emotional Changes — Understand two important developmental tasks teen undertake during this time. Part of the Teen Talk: A Survival Guide for Parents of Teens series.

Teen brain development — Learn about why your teenager may have trouble making plans, strategizing smart choices, and making good judgments. Part of the Teen Talk: A Survival Guide for Parents of Teens series.

The Teen Years ExplainedClea McNeely, PhD and Jayne Blanchard — This e-book can help both teens and adults to understand developmental changes and tips for how to apply this knowledge to your everyday life.

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