While numerous studies focus on gender gaps in wages and career opportunities, the pay gap between mothers and childless women is found to be even bigger than the pay gap between women and men, according to Sociologist Shelly Correll, Stephen Benard, and In Paik.

To carry out their study, they used fake resumes for two equally qualified female candidates - one childless, and one a mother. The researchers found that the mother was 100% less likely to be hired when she applied for a position, compared to the childless woman.

Mothers seem to be consistently ranked as less competent and less committed than women without children. "They were also offered $11,000 a year less pay, on average, than an equally qualified childless candidate," Correll says.

Men however, don't receive the same treatment - In another study, researchers used more fake resumes to apply to 638 jobs during an 18-month period. They found that childless women got 2.1 times as many callbacks as mothers with similar credentials. As for the men, there were no differences set apart for fathers and childless men.

When asked if she was surprised by the findings, Correll, who is an associate professor in the Department of Sociology at Stanford University said:
I was not surprised to find that mothers were discriminated against, but I was very surprised by the magnitude of the discrimination. With gender or race, we often talk about the subtle ways that stereotypes are disadvantaging. With mothers, the effects were huge, such as being about 100% less likely to be recommended for hire than childless women and being offered much lower starting salaries.

The Motherhood Penalty [BusinessWeek]