CERTAINLY THE HIGH rate of pregnant teens in the United States is due to a high rate of sexual activity among teens. Research shows that more than 75 percent of American girls between the ages of fifteen and nineteen are sexually active; in 1970 the number was only 29 percent. There is no one reason for the dramatic increase, say sociologists; rather, it is a combination of factors.

Dysfunctional families

Many teenage mothers—between 80 and 90 percent— come from families in which constant fighting, chemical abuse, alcoholism, or mental illness are common. To escape an unstable home life, some teenage girls are often in a hurry to find intimacy with a caring boy. "I really mostly wanted to be close," says one fourteenyear- old who has been sexually active for over a year. "I hated being at my house. My...