It might seem like a mystery at first, even a paradox: The income gap between rich and poor adults is growing, but the achievement gap between rich and poor kids is shrinking.

This was not expected. For the last few decades, adult income inequality and childhood achievement inequality both increased at the same time, and the former trend seemed to drive the latter. Rich parents can spend more money on a variety of things (e.g., summer camps, tutors, musical crib mobiles that play Chopin's “Nocturne in E-Flat”) to ensure that their kids grew up to be similarly successful. Between the 1970s and 2000s, the richest 10 percent of households more than doubled their spending per child, while the poorest third of the country could barely afford an increase.

But something important has changed recently—at least for the kids. Between 1998 and 2010, “the school readiness gap [between rich and poor kindergarteners] narrowed by 10 percent in math and 16 percent in reading,” as Sean F. Reardon, Jane Waldfogel, and Daphna Bassok write in The New York Times. The authors emphasize that this is because of better reading and math skills among poor kids, not a sudden collapse in literacy among six-year-olds in affluent private schools.

If poor parents are falling further behind rich parents, how are poor kids closing the gap? The researchers offer several explanations, like increased enrollment among state-funded preschools and low-income parents spending more time with their kids.

But here is another sudden and surprising trend that might be a factor: a great reduction in teen pregnancy between 2007 and 2013. A new study in the Journal of Adolescent Health concluded that teenagers aren’t having less sex, but they are having fewer babies, because of a significant increase in contraceptives. Reported use of the pill, condoms, IUDs, and even the withdrawal method all increased substantially in the last nine years. The key statistic: The number of teens who self-reported using no contraception fell from 20 percent to 13 percent.

This is a huge deal: The number of sexually active American teenagers using no contraception fell by 35 percent in just seven years. Meanwhile, the teen birth rate has fallen almost 50 percent since 1990.

Why might a reduction in teen pregnancy lead to higher achieving poor kids? Unintended pregnancies are concentrated among poor and less educated mothers who are younger, not married, and often not ready to devote the amount of time, money, and attention to children that rich married couples can. With better contraceptive use, poor women can plan to have children only when they’re ready to raise them.

For the past four decades, the income gap isn’t the only chasm that has opened between the rich and poor. There is also what sociologist Robert Putnam calls “Goodnight Moon time.” Rich parents spend more time with their kids, and this time make a huge difference in early childhood.

In the 1970s, rich and poor mothers both had children in their early 20s. More recently, however, college graduates become moms in their late 20s or early 30s, on average, while moms with just a high-school education or less become moms at the average age of 19, according to Putnam’s book Our Kids. "Children of less educated parents are increasingly entering the world as an unplanned surprise (complete or not, pleasant or not), while children of more educated parents are increasingly entering the world as a long-planned objective," Putnam wrote.

The fact that an enormous number of poor kids arrive as “surprises” has two important implications. The first is that poor kids don’t just have less money, they have fewer dedicated parents, too. An astonishing 65 percent of all mothers with no more than a high-school degree are unmarried at the time of their child's birth; that figure has tripled since 1980. (By comparison, 90 percent of new moms who finished college are married.) Too often, rich kids have two intentional parents armed with childrearing books and newfangled toys for infants, while poor kids have one accidental parent armed with none of that.

That leads to the second major implication of the parent gap, which is attention. Children born to poor single mothers receive less enrichment spending, are less likely to attend daycare or pre-K, hear fewer words and read fewer books at home, have fewer interactions in the house, and, perhaps most critically, spend much less time with their parents, often because the mother is working and a father is not a permanent member of the nuclear family. As a result, these children get television rather than attentive parenting. As Putnam puts it: “Rich kids get more face time, while poor kids get more screen time.”

The idea here, that increased contraception use among low-income women could improve early achievement scores for poor kids, is not a new idea. Isabel V. Sawhill, the great social-mobility researcher based out of Brookings, has a whole book dedicated to the problem of poor women "drifting into sex and parenthood" due to unplanned pregnancies.” As she has written, early childbearing is most common in poor areas with low social mobility.

In this context, contraception is not just practical; it is empowering. With higher adoption of long-acting birth control like IUDs and implants, the entire psychology of having a baby shifts from actions to prevent pregnancy toward actions to become pregnant, as Emily Bazelon wrote in her review of the Sawhill book in The Atlantic in 2014. U.S. family policy has struggled to revive marriage among poor Americans. But greater adoption of long-acting and reversible birth control technology would make motherhood more intentional. “Changing the norm from childbearing by default to childbearing by design might have a big effect on the opportunity gap,” Putnam writes.

Linking contraception with social outcomes is often controversial. Several years ago, the authors of Freakonomics pointed to another positive effect of reducing unintended births. They suggested that the Supreme Court decision on abortion in Roe v. Wade reduced unwanted pregnancies and, a generation later, crime rates fell, because children who were never born would have otherwise grown up to commit crimes. But this highly controversial claim has been puzzled over, attacked, and arguably debunked. Yet this connection between contraception and social mobility—the ability of older, wealthier, and more intentional mothers to raise higher-achieving children—is, for now, a more plausible theory.

Condoms alone will not restore the American Dream for today’s low-income families. The lesson here is not that IUDs obviate income transfers to the poor or inclusive housing policy in rich metros. The lesson, instead, is that improvements in early childhood achievement (and, with luck, those children’s adult outcomes) can come from surprising places. Perhaps birth control doesn’t just give women power over their own future; it empowers their future children, as well.