It’s fitting that Hillary Clinton’s key victories on Super Tuesday came just one week before International Women’s Day, a celebration of women’s social, economic, cultural and political achievements.

In many fields, women are making modest advances into leadership positions. Twenty-six percent of college presidents are women. Among business school leaders, women hold nearly 20% of dean positions. They represent one in five partners in private law firms, and make up a quarter of U.S. federal court judges. And, for the first time, more than 100 women serve in Congress.

In sharp contrast, female advancement through the corporate structure is stagnant. Women currently hold only 4% of Fortune 500 CEO roles. By the end of this year, there will be 23 females serving as CEOs of Fortune 500 companies — the same number as last year, and one fewer than the year before. Only one woman every two years joins the list of CEOs of S&P 500 companies.

Advancing women into positions of corporate leadership isn’t just the right thing to do—it’s also good business. Two recent surveys found that firms with more women throughout the corporate structure are more profitable, and companies with female chief executives record better stock market returns.

What should the business world do to catalyze the growth of female leadership? It requires a three-pronged approach that focuses on the boardroom, workplace sponsorship, and business education.

Growing the number of women in the executive corridor starts with the boardroom. Research shows a strong correlation between the number of women serving on boards and leading in the C-Suite. Having female board members not only encourages more women to pursue executive positions, but also provides the opportunity to facilitate real change within companies that help women advance. With women holding almost 20% of board seats in the U.S., their growing presence is promising. Fortune 500 companies with both a female CEO and a diverse board, like General Motors gm and Hewlett-Packard hpe , provide reason for optimism.

 

Career success and advancement for young professionals also relies in part on strong role models and mentors. There’s evidence, however, that corporate mentoring programs don’t necessarily serve women as well as they serve men —and that sponsorship may be an even more effective tool. This means not only coaching young women to take on complex projects they otherwise might not, but also advocating for them to move into positions of increasing responsibility. The power of sponsorship lies in realizing opportunities, gaining confidence, and supporting an individual’s potential. It is the obligation of leaders — both male and female — to serve as sponsors for women in their organizations.

But women can be effective in the boardroom and advance to executive roles only if they’ve been prepared early in their careers for success. There needs to be a concerted effort to foster young women’s interest in business. This, in turn, requires leading schools to increase female enrollment and broaden opportunities for women to develop the skills that are expected in our global business leaders. As a member of the senior leadership at a graduate business school with a student body of 50% women, I witness — every day — the importance of female representation at the critical stages of their business education.

Young women are searching for leaders who look like them at the front of their classrooms or on the board of their dream company. They need to study alongside other accomplished women as their peers and have the opportunity to lead student clubs and organizations. When combined, these educational experiences mean that more women will feel prepared to join the likes of Ginni Rometty of IBM ibm , Marillyn Hewson of Lockheed Martin lmt , and Safra Catz of Oracle orcl .

The narrative about women in public office and business has advanced in recent years in the right direction, with leaders from the private and public sector acknowledging that there is more work to do. But bold pronouncements only take us so far, and the numbers back this up: Not enough women are making it into senior leadership positions in business. This makes the call to action from International Women’s Day for worldwide gender parity timely. The business sector must act to shift the paradigm in business education and corporate leadership to support women all the way to the top.

Kate R. Salop is senior administrative dean at Brandeis International Business School located in Waltham, Massachusetts.