Puberty involves more than just the development of the secondary sexual characteristics; it also includes the major physical growth phase of human development. The shape, height and strength of teens' bodies will change dramatically from the start of puberty to the time they leave it behind.
Boys will see a few periods of distinct growth during puberty. The first growth spurt generally occurs when boys first enter puberty, sometime between 10 and 11 years old. However, their largest growth spurt will usually happen around two years after they've started puberty. During this growth spurt, which can last two to three years, boys grow on average around 3.5 inches (roughly 9 centimeters). This growth spurt will leave him close to his full adult height. Boys will have a final growth spurt toward the very end of their puberty at the end of their teens. However, between these two growth spurts, boys will also have a strength spurt, during which they will increase in muscle mass and their shoulders will widen.
However, boys won't just see an increase in their height and muscle mass; their sexual organs will grow, as well. One of the earliest signs of puberty is an increase in the size of the testicles. As they continue through puberty, a boy's testicles will continue to grow, along with the size of his penis (both in terms of length and circumference).
Girls will experience their growth spurt over their early pubertal years. Most girls will start growing taller during ages nine years old through 14.5 years old, reaching their peak adolescent height around age 12 years. Girls don't necessarily increase in muscle mass, but they do start adding weight as their body fat increases, most notably as hips become curvier and their breasts develop.