Is the boardroom the last glass ceiling?

October 10, 2013, 12:11 PM UTC

While the tally of female Fortune 500 CEOs grows steadily and the bar to get on Fortune’s Most Powerful Women list rises higher every year, there is one critical place where women aren’t advancing much at all: the boardroom.

In 2012, 16.6% of Fortune 500 company directors were women, according to Catalyst. That’s up from 13.6% in 2003. But the upward slope has flatlined for the past seven years.

The most common excuse — that there aren’t enough qualified female candidates — doesn’t rate. As former Ernst & Young CEO Jim Turley, who recently joined the boards of Citigroup (C) and Emerson Electric (EMR), says, “Over half of college graduates today are women — and well over half of the best graduates are women. If we’re going after the best talent, we need to put more women on boards.”

At the SAIS Global Conference on Women in the Boardroom at Johns Hopkins’s School of Advanced International Studies in September, Turley was on one of three panels I moderated. Some good ideas came out of the discussions. Here are three:

Reimagine the talent pool. When Kerry Clark was CEO of Cardinal Health (CAH) and adding to his board a few years ago, he wanted a woman but couldn’t find one in the senior corporate ranks. Bonnie Gwin at search firm Heidrick & Struggles urged Clark to consider candidates who would someday sit at the top of the org chart. She introduced Clark to an IBM (IBM) general manager named Colleen Arnold, who turned out to be an excellent director, he says. Arnold’s rise at IBM has continued apace. She’s now an SVP in IBM’s global business services unit.

MORE: Most Powerful Women – Full list

View work on boards as career development. While many Fortune 500 CEOs don’t allow their executives to serve on outside boards, Marge Magner calls board work “a development opportunity.” Magner, on Fortune’s MPW list when she was at Citigroup, is now nonexecutive chairman of Gannett (GCI) as well as a director at Accenture (ACN) and Ally Financia (ALFI)l. Turley, too, thinks CEOs should encourage direct reports to join boards. “Serving on boards hones their skills and makes them better leaders,” he says.

Set targets for board composition. Corporate America will never go the way of Norway, which mandates that women occupy 40% of public board seats. But the U.S. can learn from the U.K., where former trade minister Lord Mervyn Davies leads a task force to get more women on boards. Since early 2011, Davies has met with dozens of FTSE 100 CEOs and asked them to aim for at least 25% female representation on boards by 2015 — and disclose progress along the way. The results so far are impressive: 17.3% of FTSE 100 directors are women, up from 10.5% just three years ago, suggesting that sunlight (and a nudge from a powerful politician) may be the best solution to a persistent problem.

This story is from the October 28, 2013 issue of Fortune.