Kids go through astonishing physical changes in elementary and middle school. They'll grow about 2.5 inches every year until they hit a growth spurt in early adolescence. You'll start to see early signs of puberty, including pubic hair and the growth of sex organs, starting around age 8 or 9 for girls and age 10 or 11 for boys. They also get a whole new set of teeth! Between ages 6 or 7 and 12 or 13, children lose 20 teeth and grow back 28 teeth (32 counting wisdom teeth that may develop in early adulthood).