A 2016 study by Robert Mare at the University of California, Los Angeles, lent credence to our expectation. Mare found that there has been an increase in assortative mating in recent years—spouses are more likely to have similar levels of education today than they used to. Logically it would seem that similar levels of education should lead to similar levels of career success. That is, when two MBAs get married, both are poised to become business executives and produce lots of little MBA-procuring children. But of the 39 women we graduated with who are either married or partnered, only 4 fit the classic power couple description: A chief marketing officer at a bank married a corporate real-estate vice president; a sought-after screenwriter married a music executive; a wealth manager at a large investment bank married a brokerage executive; and a prominent doctor married a general counsel at a brokerage firm.

We believe that couples often behave as though there is a set limit on the amount of ambition that can be contained within one union. Sometimes this limit is clearly articulated; sometimes it is unspoken, and the ambition can be distributed in different ways. Some couples consist of a high-achieving woman married to a man who has chosen to stay at home with the children, and sometimes it’s the reverse. Sometimes both members of the couple have careers that they’ve decided to scale back in order to be more available to children, or to pursue other passions like volunteering or hiking. But with only a few exceptions, our former classmates either consciously chose or happened into marriages that supported what feels like a finite cap on career ambition.

But, the assortative mating theory still holds. While nearly all of our highest achievers paired off with men who had comparable degrees, once they became parents ultimately only one person in the couple ended up with a classically successful career. The other spouse opted to stay home with the children, or to have a career with flexible hours that enabled them to be the primary caregiver. It is almost as though, in families where someone has a big job, all of the career ambition has been allocated to one person. So while nearly all of our stay-at-home contingent are married to high–achieving spouses (which in some cases led them to choose to stay at home), our highest achievers are almost exclusively married to stay-at-home fathers or men who have scaled back their careers.

In terms of numbers: We have eight high achievers who are married with children; five of them are the sole or primary wage-earner in the household. None of our former classmates who are Scale Backers or Opt Outers are married to stay-at-home fathers. A 2015 Pew Research study reports that 7 percent of American fathers are stay-at-home dads, which is roughly in line with the 8 percent of our former classmates married to men who do not work outside the home and are the primary caregiver. But for this group, only the high achievers are married to stay-at-home dads.