When it comes to climbing the corporate ladder, the hardest part for many women is stepping onto that first rung.

That’s a key finding of the latest Women in the Workplace study by McKinsey & Company and the nonprofit LeanIn.org, which analyzed the human resources practices of more than 300 companies employing more than 13 million people.

According to the report [PDF], the presence of women in management roles is showing the most improvement at the top. Currently, 21 percent of C-suite roles in the companies surveyed are held by women, up from 17 percent in 2015. That’s a 24 percent increase in four years.

But further down, women are underrepresented at all levels, and the pace of improvement has been slower. A widening gap between men and women starts at the first level of management and gets worse from there. At the entry level, men still outnumber women by a small measure (51 percent to 48 percent), but at the manager level, the mix shifts substantially: only 39 percent of managers are women—which represents only  a 3 percent improvement since 2014. For every 100 men who are hired and promoted to a managerial role, 72 women get the same opportunity, the report states.

At each increasing level of seniority, women make up a smaller share of the roles. Women of color are particularly underrepresented in management, holding only 12 percent of manager positions and 4 percent of C-suite jobs.

Although the significant jump in C-suite representation “is a step in the right direction, parity remains out of reach,” the report states. “Women—and particularly women of color—are underrepresented at every level. And without fundamental changes early in the pipeline, gains in women’s representation will ultimately stall.”

Carolyn Tastad, group president of Procter & Gamble’s North American operations, told the Wall Street Journal that the obstacles to women’s advancement start far earlier than many corporate leaders may realize.

“Bias still gets in the way—bias of who you know, who’s like you, or who performs and operates the same way you perform and operate, whose style is more similar,” she said.

Meanwhile, most HR teams aren’t focusing on improving lower-level management opportunities for women, the study found. “When asked what the biggest challenges are to getting to equal numbers of women and men in leadership, awareness of the promotion gap at the first step up to manager is low,” the report states. “HR leaders more often point to less access to sponsorship or a lack of qualified women in the pipeline.”

The report, which also covers cultural and identity issues, recommends that organizations set a goal for moving more women into management; require diverse slates for hiring and promotions; and implement training to combat unconscious bias.

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