Physical Development Stages

Breaking tasks up into smaller pieces makes them more manageable to accomplish and also makes it much easier to track progress. The same idea works for learning about and tracking physical development—stages make it easier to check in on how things are moving along. Some physical development stages even include a few smaller stages of their own. This can help parents and doctors make sure babies are developing normally and give teenagers an idea of when puberty will finally be over.


Physical development researchers separate childhood in three smaller stages: early childhood, middle childhood and late childhood. Childhood’s beginning and end are both dependent on specific criteria—it covers from birth until puberty starts. In general, the transitions between the stages that make up childhood have less clear boundaries and are in fact somewhat arbitrarily assigned. The exception to this is within early childhood. Early childhood covers infancy and toddler-hood. In their book “Human Motor Development,” professors V. Payne and Larry Issacs write boys weigh 7.5 lbs average birth; girls 7 lbs. Before reaching toddler-hood, at around one year of age, both boys’ and girls’ weights triple. Infants get much taller too. With birth lengths of about 20 inches, boys and girls grow to about 30 inches by their first birthday.

Toddler-hood begins when a child begins walking and covers until age four and early childhood extends to age seven. Middle childhood covers from age seven until nine and late childhood from nine years until puberty begins. The growth rates for both height and weight slow through toddler-hood and the rest of childhood—not accelerating again until puberty hits.


During adolescence, the body undergoes major physical changes because of puberty. These changes include getting taller and heavier very quickly. Statistics from “Human Motor Development” show during the first three years of adolescence boys gain 45 lbs. and girls gain 35 lbs. Height also increases rapidly. During puberty both boys and girls gain almost 20 percent of their total adult adult height. Growth slows through the rest of adolescence. Data supplied by the Centers for Disease Control and Prevention show by the time children stop getting taller the average male 69 reaches inches tall and the average female 64 inches. Adolescence, as a physical development stage, ends when height stops increase. For girls, the average age is 17 years old and for boys, the average age is 20.


Similar to childhood, adulthood divides into three short categories: early adulthood, middle adulthood and late adulthood. There are no clear lines or benchmarks for the transition between these shorter stages. Adulthood begins when height stops increasing and while most parents might disagree with this–from a physical development perspective at least–it’s true. The arbitrary age used to separate early adulthood from middle adulthood is 40 years old. Sixty years old marks separates middle adulthood from late adulthood.

About this Author

Aaron Jacobsen specializes in writing about health, fitness and mental performance topics for various websites. He holds a master’s degree in kinesiology and is a former faculty member at San Jose University.