Understanding Adolescence 1: A Time of Change

Adolescents have one foot in childhood and one foot in adulthood. This publication, the first in a three-part series, explores the biological changes that occur during adolescence.
Understanding Adolescence 1: A Time of Change - Articles
Understanding Adolescence 1: A Time of Change

Adolescents are young people who straddle the fence between childhood and adulthood. They have one foot secured in childhood and one foot moving into the world of adulthood.

Adolescence is a unique period of the human life span. In fact, no other developmental period, with the possible exception of infancy, is characterized by so many complex changes. These changes include:

  • very fast physical growth
  • the rise of reproductive sexuality
  • new social roles
  • growth in thinking, feeling, and morals
  • school transitions

This is the first of a three-part series of bulletins that explore adolescence. They are divided into the following major topics:

  1. The definition of adolescence and the biological changes that occur during that period.
  2. The major questions facing adolescents as they search for themselves.
  3. The developmental tasks that adolescents must accomplish as they mature.

The information in this series serves as a “road map” of what to expect from adolescents. Using this road map, parents and other adults can determine whether adolescents are reaching their desired destinations, or whether they have detoured and need extra support and intervention to get them back on track. Parents and adults who work with adolescents must remain sensitive to adolescents’ individual needs, because they develop at varying rates.

This series also provides information about parent-adolescent communication. Positive interaction with your adolescents can enhance their development.

What Is Adolescence?

Adolescence begins with biological maturation (puberty), when young people must accomplish developmental tasks and develop a sense of personal identity. It ends when young people achieve self-sufficient adult-hood as defined by society.

Adolescence has three substages: early adolescence, middle adolescence, and late adolescence. In early adolescence, between 10 and 14 years of age, adolescents are moving from elementary school to middle or junior high school. Middle adolescence is between ages 15 and 17, and late adolescence lasts from age 18 to the early twenties. Late adolescence seems to be extending further into the early twenties; this is especially true for those adolescents who cannot support themselves financially after high school. For the purposes of this guide, we will group middle and late adolescents together and refer to them as late adolescents.

The difference between early and late adolescence can be illustrated by comparing 11- and 12-year-olds with 17- and 18-year-olds. Early adolescents are barely out of childhood. Much like younger children, they still need special nurturing and protection. Late adolescents, on the other hand, share many attributes of adults. Early and late adolescents have very little in common with each other, and their needs and abilities tend to differ. Parents and other adults who work with youth need to be aware of these differences in order to provide the support necessary for healthy adolescent development.

What Are the Biological and Physical Changes That Occur During Adolescence?

The completion of biological and physical development associated with adolescence seems to occur earlier now than in the past, roughly 2 years earlier than in the 1900s. Puberty, which signals the beginning of adolescence, is a developmental process that takes about 2 to 4 years to complete. Puberty usually begins 2 years earlier for girls than for boys, and girls are generally taller than boys their age until around age 14, when boys are generally taller.

The events most closely associated with puberty, menstruation in girls and ejaculation in boys, actually occur approximately midway in the develop-mental process. Girls are generally 12 years old at the onset of menstruation (menarche). Boys are on average 13 years old at first ejaculation. However, it is important to remember that these ages can vary.

Sexual dimorphism—the emergence of physical differences, such as height, weight, body proportions, and reproductive systems, between men and women—occurs during puberty.

Sex hormones, specifically estrogens in girls and androgens in boys, increase during this period. Due to higher levels of androgens in their systems, boys generally suffer more acne and odor problems than girls do. At approximately age 15 for girls and ages 16 to 17 for boys, hormone production levels off.

Early adolescent girls (10 to 14 years old) experience:

  • onset of menstruation at age 12 on average
  • a growth spurt of approximately 8 to 10 inches
  • weight gain and an increase in muscular development
  • changes in body proportions—hips widen
  • development of breast buds and pubic hair

Middle and late adolescent girls (14 to 17 years old) experience:

  • full expression of secondary physical characteristics
  • full development of breasts
  • development of sweat glands and oil glands (acne and odors)

Early and middle adolescent boys (12 to 16 years old) experience:

  • a growth spurt of approximately 12 to 13 inches
  • weight gain and an increase in muscular development
  • changes in body proportions—shoulders broaden
  • development of pubic hair

Middle and late adolescent boys (16 to 20 years old) experience:

  • full expression of secondary physical characteristics
  • development of facial hair
  • development of sweat glands and oil glands (acne and odors)


Adolescence is a complex period in the life span, marked by a multitude of changes. These changes make adolescence an exciting, as well as awkward, time in one’s life. Adolescents often are easily embarrassed and may grow uncomfortable with childish routines, such as kissing parents goodnight. While adolescents may look like adults, we know that they are not. They need time and opportunities to understand them-selves, their new bodies, new roles, and new relationships. For parents and adults who interact with adolescents, it is important to know about the normal changes in the bodies and behaviors of adolescents. Awareness of these facts enables parents and other adults to provide better support for the adolescents in their lives.

Parents and adults should expect ambiguity, uncertainty, and exploration/experimentation when interacting with adolescents. Parents need to spend time with adolescents, while respecting their privacy at the same time. Through example and guidance, parents and adults can have a strong positive impact on the lives of adolescents.

The first bulletin of this three-part series has only begun to show the complexity of the changes that confront individuals as they begin their second decade of life. The next two bulletins will provide more information about the intellectual and emotional changes and challenges that arise in adolescence.


Lerner, R. M., and N. L. Galambos (Eds.) (1984). Experiencing adolescents: A sourcebook for parents, teachers, and teens. New York: Teachers College.

Vernon, A., and R. H. Al-Mabuk (1995). What growing up is all about: A parent’s guide to child and adolescent development. Champaign, IL: Research Press.

The WonderWise Parent contains information on parenting and parent-child relationships.


Carnegie Council on Adolescent Development (1995). Great transitions: Preparing adolescents for a new century. New York: Carnegie Corporation.

Cobb, N. J. (1996). Adolescence: Continuity, change, and diversity. Mountain View, CA: Mayfield Publishing.

Hamburg, B. (1974). “Early adolescence: A specific and stressful stage of the life cycle.” In G. Coehol, D. A. Hamburg, and J. E. Adams (Eds.), Coping and adaptation (pp. 101-125). New York: Basic Books.

Lerner, R. M. (1995). America’s youth in crisis: Challenges and options for programs and policies. Thousand Oaks, CA: Sage.

Petersen, A. C. (1987). “The nature of biological-psychological interaction: The sample case of early adolescence.” In R. M. Lerner and T. T. Foch (Eds.), Biological-psychosocial interactions in early adolescence: A life-span perspective (pp. 35-62). Hillsdale, NJ: Erlbaum.

Simmons, R. G., and D. A. Blyth (1987). Moving into adolescence: The impact of pubertal change and school context. New York: Aldine DeGruyter.

Prepared by Daniel F. Perkins, associate professor of family and youth resiliency and policy in the Department of Agricultural and Extension Education.


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