A large body of research shows that the children of single mothers are more likely than similar children with married parents to experience childhood poverty, act up in class, become teenage parents and drop out of school. Married couples are having children later than they used to, divorcing less and investing heavily in parenting time. By contrast, a growing share of single mothers have never married, and many have children with more than one man. The people with more education tend to have stable family structures with committed, involved fathers. The people with less education are more likely to have complex, unstable situations involving men who come and go. Nearly half the unmarried parents living together at a child’s birth split up within five years. The growth in single parenthood in recent decades has accounted for 15% to 40% of the widening income gaps. As recently as 1990, just 10% of the births to white women with some post-secondary schooling but not a full college degree occurred outside marriage. Now it has tripled to 30%, compared with just 8% for women of all races with college degrees. Less-educated women are also more likely to have children with more than one man. A third of those with high school degrees or less already had children with multiple men. So did 12% of mothers with some post-high-school training. Women who have finished college before giving birth are unlikely to have children with multiple men. Having men in the house for a short time with ambiguous parenting roles can be really disruptive for children. Among children raised in the poorest third as teenagers, 58% living with two parents moved up to a higher level as adults, compared with just 44% of those with an absent parent. Just 15% of teenagers living with two parents fell to the bottom third, compared with 27% of teenagers without both parents. You’re more likely to rise out of the bottom if you live with two parents, and you’re less likely to fall out of the top. Researchers have found that marriage itself can have a motivating effect, pushing men to earn more than unmarried peers. Marriage, that is, can help make men marriageable.