In most cases, research shows that mentors who just offer advice and help build confidence aren't enough. Companies must ensure that women have sponsors who make it a personal goal to actively advocate for their female employee during key personnel decisions. Many programs tend to emphasize mentoring, because fostering sponsor relationships is harder and can take more time.

In an effort to forge those relationships, Bain & Company has paired hundreds of women with sponsors since 2014, something the firm partly credits with doubling the number of women it has at the manager level or higher.