The Cornell study's methodology was simple. Researchers sent out nearly identical résumés to hundreds of employers. The résumés differed only in facts about the purported applicant's personal life: some were moms, and some were childless. What researchers found was shocking. Based solely on the information in the job applications, employers rated mothers as significantly less competent and committed than their childless counterparts, even though the accomplishments and experience on the résumé were exactly the same.
That's not all. The study also concluded that prospective employers offered starting salaries worth $11,000 less to moms than to childless women. Even without factoring in annual salary increases or promotions, the difference may equate to hundreds of thousands of dollars less over a mother's career. Citing the same study, the Boston Globe recently reported that "mothers earn 5 percent less per child than other comparable workers."
It can be harder for working moms to get back into the workforce, too. Less than half of mothers get callbacks for interviews, as compared to childless workers. And the Cornell study found a massive discrepancy between the hiring statistics for their hypothetical applicants: "...while participants recommend 84% of female nonmothers for hire, they recommend a significantly lower 47% of mothers."
Ironically, the Cornell study also found that working fathers benefit from the perception of their commitment and competence, as opposed to childless men. Employers were also more generous when it came to the work/life balance of working dads. "Fathers were allowed to be late to work significantly more times than nonfathers. Finally, they were offered significantly higher salaries than nonfathers."
So why do working moms make less? The Cornell study speculated that employers "may assume that women who have apparently forgone childbearing to enter the labor market are extraordinarily committed to work," yet concluded that "interruptions from work, working part-time, and decreased seniority/experience collectively explain no more than about one-third of the motherhood penalty." In other words, there is no good reason for the motherhood penalty. All we know for sure is that the penalty is real, and it is severe.