It has long been assumed that the residual gap in earnings between men and women (after controlling for productivity characteristics, occupation and industry segregation, and union membership status) is due to gender discrimination. A growing body of evidence, however, suggests that it may also reflect the effect of having children.
According to this research, employed mothers now account for most of the gender gap in wages (Glass 2004). In the U.S., controlling for work experience, hourly wages of mothers are approximately four percent lower for each child they have, compared to the wages of non-mothers (Budig and England, 2001). The magnitude of these family effects differs across countries, but, in general, men accrue modest earnings premiums for fatherhood, whereas women incur significant earnings penalties for motherhood (Waldfogel, 1998; Harkness and Waldfogel, 2003; Sigle-Rushton and Waldfogel, 2007; Budig and Hodges, 2010; Hodges and Budig, 2010; Smith Koslowski, 2011).
The size of the penalty seems also to vary by whether women and men are toward the top or bottom of the employment hierarchies of skills and wages, and it also varies across countries (England et al. 2014; Cooke 2014). The findings in this area are sometimes inconsistent, however, and suggest that there is a need to include a combination of skills and wages (England et al. 2014) and to choose carefully measures of job interruptions (Staff and Mortimer, 2012).