Finally, we’re getting somewhere.

For years, experts have trotted out a series of surely related but still unsatisfying reasons women aren’t getting paid the same as men and aren’t getting the same number of leadership jobs. They need more flexibility! (So do men.) They opt out and have babies! (So why is pay lower even for 23-year-old female grads?) They aren’t getting as many advanced degrees! (Uh, yes they are.)

But a new report released Wednesday from Catalyst, the research organization that studies and advises companies on women’s advancement in the workplace, adds a much more logical reason to this longstanding puzzle: Women simply aren’t getting the “hot” jobs. When they’re not being placed on highly visible projects, in key international roles or in critical profit-and-loss management positions, they’re never going to reach the top leadership ranks to which such high-profile stretch assignments typically lead.

The numbers are telling. In a longitudinal study of 1,660 MBA graduates—a group of men and women already primed to hold such “hot jobs”—Catalyst found that the men in the group reported leading projects with bigger budgets (more than twice the size of women’s), larger teams (more than three times as many staff), higher risk profiles (30 percent of men vs. 22 percent of women said their project posed a greater risk) and more visibility to the C-suite (35 percent of men vs. 26 percent of women reported having this exposure).

The differences are not, however, due to less appetite for risk or willingness to relocate for international jobs, Catalyst found. Significantly more men than women (88 percent vs. 77 percent) were assigned to work on global teams that did not require relocation. Even though they found that women are generally less willing to make a move than men, when Catalyst looked solely at the group who raised their hands to move, men still got more “employer-initiated” international assignments.

Yet, interestingly, women are getting more access than men to certain development opportunities. Within 18 months of completing a leadership development program, 47 percent of women versus 39 percent of men were assigned a mentor. Women also were assigned to leadership development programs earlier than men, and participated in longer programs than their male counterparts.

But all this leadership training that companies are rushing to give women could be setting up a false sense of security—namely, that companies are doing something to address the problem. Mentors are great if they’re in actual positions of power, but all too often assigned mentorship just ends up meaning awkward relationships that feel more like an obligation for both parties than an asset. And as almost anyone who’s been through a leadership training program can attest, their value can range from nearly worthless to mildly helpful. Catalyst’s survey participants seemed to agree: While 62 percent said high-profile assignments had the greatest impact on their careers, just 10 percent said training programs were the biggest factor in getting ahead.

Of course, what remains unclear is why more women aren’t getting as many “hot jobs” as men. Is it outright bias? Do women do less to negotiate for these jobs than men? Catalyst’s report does suggest that with more high-level “sponsors,” or mentors in real positions of power, men have greater access to these coveted roles. But even Catalyst acknowledges that this can’t fully explain the difference: “sponsorship,” the report’s authors write, “likely isn’t a silver bullet when it comes to closing the gender gap.”

Still, it’s encouraging to see more focus on actual jobs and experience as the reason for the lack of women at the top rather than all the chatter about work-life balance and mommy tracks and, well, “binders” full of women. Until companies do more to help talented women get high-profile assignments, rather than just stuffing the ranks of leadership development programs with young women or bragging about their work-life policies, women simply aren’t going to reach the upper echelons of Corporate America at the same rate as men. 

Jena McGregor is a columnist for the Washington Post’s On Leadership section.

More from On Leadership:

A new ‘Year of the Woman’?

Why the Petraeus affair captivates us all

What makes an excellent president

Like On Leadership? Follow us on Facebook and Twitter:

@post_lead | @jenamcgregor | @lily_cunningham