Late childhood is generally defined as ages 9 through 12. Up until this point, most children have been growing at fairly predictable rates. Now, all bets are off due the often wild fluctuations in physical development. One preteen can be in a completely different growth phase than another child who is the exact same age. The disparity in physical development may continue well into adolescence, when growth patterns even out.
The first signs of puberty typically begin to appear in late childhood. The term puberty is used to define the approximately 5-year period of biological maturation where a boy or girl becomes able to reproduce. In girls, puberty can begin between the ages of 8 and 13, while it usually begins around age 10 in boys.
Development in Girls
The years of late childhood development can be exciting and confusing, and even a bit disillusioning. A 12-year-old girl may have a hard time understanding why her 9-year-old neighbor has already developed breast buds while she doesn't have slightest hint of a protruding chest. A preteen as young as 10 years old may experience her first menstrual period. However, the average starting age is 12.5.
Development in Boys
Boys in late childhood may notice an enlargement of the testicles and scrotum, possibly as young as age 9. A boy's penis generally starts to grow around age 12. Also around this time, boys will begin to grow pubic hair, as well as armpit, leg, chest and facial hair.
Boys & Girls
Boys and girls alike experience rapids growth spurts in late childhood. Girls begin to sprout between the ages of 9 and 14. Boys lag behind slightly at the onset, but will more than make up for it as time goes on. A boy's growth in height usually occurs between ages 10 and 18, seeing the most rapid growth typically at around age 14.
The physical development in late childhood is setting the stage for the upcoming teen years, during which time boys and girls will complete puberty and experience significant mental and cognitive development as they mature into full adulthood.