Over the past seven years, two small changes in the participation of mothers in the workforce have generated almost as much attention as the initial entry of wives and mothers into the working world in the 1960s.

Between 1998 and 2000, the labor force participation of women with babies under the age of 1 dropped for the first time in more than 30 years, falling from 59 percent to 55 percent. Then, between 2000 and 2004, the labor force participation of mothers with preschoolers also fell.

Ever since, feminists, anti-feminists and “post”-feminists have been debating the implications of this so-called “opt-out revolution.” Some rejoice that career women are finally embracing their inner housewife and using their education in the service of full-time parenting. Others are dismayed, warning women they will jeopardize future earnings and independence by retreating to the home. And still others maintain that because only affluent women can afford to stay home full-time with their children, we need to help the wives of low-income husbands to stay home too.

Much of this debate is based upon false assumptions about who stays home and why, according to a study just released by researchers associated with the Council on Contemporary Families. The highest concentration of full-time homemakers in America is found among women married to low-earning men, while highly educated wives are increasingly likely to combine work and motherhood.

Long-range trends in the United States and the rest of the industrial world suggest that there has been a fundamental, irreversible revolution in the relationship between women and work. Countries that still organize their work life and social policies around the ideal of a male breadwinner providing for a stay-at-home wife will sooner or later have to face up to this reality.

Since 1970, the involvement of women in the paid labor force has increased dramatically throughout the industrial world. In some countries, the obstacles to combining motherhood with paid employment are still so daunting that mothers must withdraw from the labor force for several years. But far from encouraging a revival of male-breadwinner families, this situation accelerates other types of family change.

For example, in Japan and Italy, the age of marriage has reached new highs and birth rates have plummeted: Single women increasingly postpone marriage and childbirth because they cannot combine motherhood with the work they have come to see as an important part of their lives. One Italian demographer says that “women no longer give up work for the family; on the contrary, they give up having children in order to have a job.” Americans may agonize about whether it’s good for society to have so many working moms, but family researchers in Japan, Italy and Singapore worry much more about having so many working non-mothers.

France and the United States, where many more mothers hold down full-time jobs, have much higher birth rates than Germany, Italy, Japan and Spain, where it is harder for mothers to work outside the home. But because America, unlike France, does not provide universal and high-quality preschool, low-income mothers in the United States often cannot afford to work. Their participation in paid labor is much lower than that of middle- and high-income mothers, whose employment rates remain at world historic highs.

In the United States, the labor force participation of mothers with preschool-age children tripled between 1960 and 1990, rising from 20 percent to 60 percent. According to Stanford researcher Paula England, the workforce participation of mothers continued to rise during the 1990s, but at a much slower rate, so that by 2000, “only” 65 percent of mothers of preschoolers were working. So the slight dip in employment of moms with babies under 1could simply mean that some mothers were taking the timeouts that are legally guaranteed to all mothers in most other industrial countries, and then going back to work.

Between 2000 and 2004, the labor force participation of mothers with children under 5 did drop slightly, from 65 to 64 percent - possibly, says economist Heather Boushey, because of a recession that saw a drop in the labor force participation of non-mothers as well. But whatever the reason, the figure was back up to 65 percent by 2006. As England says, “This is hardly an opt-out revolution.”

Some believe that the opt-out revolution would become a reality if more women could afford to stay home. But this hope is based on another misconception. The women most likely to become stay-at-home moms today are in fact the ones whose husbands can least afford to support a family. Women whose husbands’ earnings are in the bottom 25 percent are the only sector of the population where full-time mothers outnumber those who combine paid work with parenting. Fifty-two percent of these wives are out of the paid labor force, compared with only 20 percent of wives whose husbands’ earnings are in the middle range.

Many American women, then, are full-time homemakers because they cannot afford to work. They do not have the education or job experience to earn a salary that would cover the costs of child care or transportation, even though the family could really use a second income.

In families where men earn $60,000 to $120,000 a year, 72 percent of mothers work outside the home. When you get to husbands in the top 5 percent - men who earn more than $120,000 a year - 40 percent of moms stay home, presumably by choice. But even in this rarified income bracket, 60 percent of mothers work outside the home, although their families could clearly get by on their husbands’ earnings. And those who stay home often do so because their husbands’ high earnings require such long workweeks that no family functions would get done at all if the wife did not stay home to organize them.

Highly educated women are more likely to combine work with motherhood than less-educated women, and this is even more true today than in 1980, at the height of the feminist movement. As of 2006, England reports, 77 percent of mothers with college degrees were employed, compared to 71 percent of mothers with high school degrees, and just 52 percent of mothers without a high school degree. Given that women are now a majority of those who earn college degrees, it is unlikely that we will see a decrease in the labor force participation of mothers in the coming decades.

Women are in the workforce to stay. Where employers and policy-makers refuse to accommodate women’s desire to combine work and family, we see one of two outcomes: Either women stop having babies, as in Italy or Japan, or, as in the United States, many women who need to work can’t afford to (because of expensive and uneven-quality child care) and many women who want to work feel guilty about the choices they are forced to make.