Such policies contribute to these countries’ swollen welfare states and higher tax burdens, but they do keep women at work. Back in 1990, in a ranking of 22 developed countries, the United States had the 6th-highest share of its prime-working-age women active in the work force. By 2010, it had tumbled to 17th place. A new study from Francine D. Blau and Lawrence M. Kahn, both economists at Cornell, estimates that if the United States had the average of other developed countries’ work-life policies, 82 percent of America’s prime-working-age women would be in the labor force, instead of the current 75 percent.

But what kind of employment would they have, exactly? New research suggests that, because it’s primarily women who take advantage of leave and part-time entitlements, work-life accommodations often paradoxically limit career trajectories. Women in Sweden, Finland and Denmark — and other countries held up as paragons of gender parity — are much more likely to end up in traditional pink-collar positions than are their counterparts in the United States. They are certainly much less likely to end up as managers, or in traditionally male professional arenas like law or finance. “In a regime where anyone can go part time, where it’s hard to get rid of people if they do, employers might sort on the front end and not hire people they think are likely to want to go part time, which usually means women,” said Lawrence F. Katz, an economist at Harvard. “There may be no way a woman can credibly commit to sticking around and not going part time.” The U.S., where these policies do not exist, has the smallest gap between women’s representation in the labor force and their representation in senior management positions.

In order to prescribe policies that really allow female workers to “lean in” at work, social scientists are trying to find ones that recast social norms and encourage male workers to “lean in” at home. One area where there seems to be a lot of potential is paternity leave, which still has a stigma in both the United States and Europe. To remedy this bad rap, countries like Sweden and Norway have recently introduced a quota of paid parental leave available only to fathers. If dads don’t take it, they’re leaving money on the table. In Germany and Portugal, moms get bonus weeks of maternity leave if their husbands take a minimum amount of paternity leave. All these countries have seen gigantic increases in the share of fathers who go on leave.

This might not sound like such a big deal, but social scientists are coming around to the notion that a man spending a few weeks at home with his newborn can help recast expectations and gender roles, at work and home, for a long time. A striking new study by a Cornell graduate student, Ankita Patnaik, based on a new paid paternity-leave quota in Quebec, found that parents’ time use changed significantly. Several years after being exposed to the reform, fathers spent more time in child care and domestic work — particularly “time-inflexible” chores, like cooking, that cut into working hours — than fathers who weren’t exposed to the reform. More important, mothers spent considerably more time at work growing their careers and contributing more to the economy, all without any public mandates or shaming.

Paid paternity leave, like paid maternity leave, may sound like a pipe dream, but states (New Jersey, California) and big companies (Ernst & Young, Bank of America) are increasingly offering it and financing it out of their own pocket. They have a vested interest in lobbying Congress to federalize the costs of these accommodations. And that seems only fair. After all, unleashing the full potential of the second sex benefits not only this handful of players but the entire U.S. economy, too.