Improved motor skills
As adolescents continue to mature they become better able to move their bodies with greater skill and precision. These movement skills are divided into two types: gross motor skills and fine motor skills. Gross motor skills refer to the large muscle movements of the body (e.g. muscles used while running), while fine motor skills refer to the tiny and precise muscle movements (e.g. muscles used while keyboarding or texting). Relative to boys, adolescent girls make only modest gains in their gross and fine motor skills until approximately 14 years of age. After this point, they generally do not experience any additional improvement in their motor skills unless they are specifically training for a sport or hobby which requires these skills. In contrast to girls, the motor skills of adolescent boys continue to improve, particularly gross motor skills. Adolescent boys rapidly gain physical speed, jumping strength, throwing strength, and endurance throughout the entire period of adolescence, even into their early 20's.
Primary sexual characteristics
Besides these changes in height, body composition, and motor skills, the sexual reproductive system triggers many changes during the transition from childhood to adulthood. Young teens develop both primary and secondary sexual characteristics that are brought about by hormonal changes. Primary sexual characteristics refer to the reproductive organs themselves; e.g., the ovaries and testes. Secondary sexual characteristics refer to other characteristic indicators of adult male and female bodies (e.g., body hair). The development of primary sexual characteristics indicates youth have become capable of adult reproductive functioning (i.e., the ability to make babies). The development of both primary and secondary sexual characteristics begins during late childhood and continues throughout early adolescence. However, it is important to remember youth experience these changes at different rates and times. For more information about the biological and hormonal changes that trigger these changes, and for suggestions about guiding young teens through this process, please refer to the article on Puberty in the Middle Childhood series.
For females, the most significant primary sexual characteristic is the first menarche, or first menstrual period. The first menarche indicates girls have begun to ovulate; i.e., to release mature eggs that can become fertilized by male sperm through sexual intercourse. The average age for the first menstrual period is 12 years, but girls can reach menarche at any age from 10 to 15 years old and still be considered "normal."
For males, the primary sexual characteristics include an enlargement of the penis and testes, and the first spermarche; i.e., the first ejaculation of mature sperm capable of fertilizing female eggs through sexual intercourse. The average age of first spermarche is 13 years, but it can occur anytime between the ages of 12 and 16 years. On average, the testes will begin to enlarge at about 11 years of age, but this growth can occur anytime between 9 and 13 years. On average, the penis begins to enlarge around age 12, but this growth can begin at any age between 10 and 14 years. The penis reaches its adult size at about age 14, but this can occur anytime between the ages 12 and 16.
Secondary sexual characteristics
Like primary sexual characteristics, secondary sexual characteristics are brought about by the hormonal changes associated with the maturing reproductive system and include changes in body hair and changes in voice quality. Young adolescents will notice hair growing in new places on their bodies, such as their underarms and groins. While this process began during late childhood, this hair continues to thicken and darken during the teen years. Teen guys will notice their facial hair continues to grow more quickly and more thickly, and they may notice hair growing on their chest and stomach. This hair may continue to grow thicker until middle or late adolescence.
Teen guys will also notice their voices begin to deepen between ages 12 to 15 years. This happens as their vocal cords grow longer, and their larynxes, or voice boxes, grow larger. The enlarged voice organs cause deeper voice tones. Adolescent guys will notice their "Adam's apples," grows larger during this period. This is because the enlarged larynxes push out the piece of cartilage in front of the larynx. Everyone has this piece of cartilage, but it's not noticeable in females because of their smaller voice boxes. This change can be unnerving for many guys because at the beginning of this change, their voices may crack, or unexpectedly squeak during speech. This can cause unwanted attention and can be embarrassing. Male adolescent voices can continue to gradually deepen well into late adolescence.