KPMG also found that for more than half the women who joined all-male California boards in 2019, those board seats were their first, evidence that the law had worked to broaden the candidate pool.

In the private sphere, financial firms and investors are now demanding that their clients have diverse boards. In January, David Solomon, chief executive of Goldman Sachs, which was the largest underwriter of public offerings in 2019, announced that starting on July 1 the bank wouldn’t take a company public unless “there’s at least one diverse board candidate, with a focus on women.” In 2021, Goldman Sachs will raise its requirement to two.

“We might miss some business, but in the long run, this I think is the best advice for companies that want to drive premium returns for their shareholders over time,” Solomon said.

His announcement echoed a similar sentiment from Larry Fink, chief executive of BlackRock, who in 2018 wrote in his annual letter to chief executives that “boards with a diverse mix of genders, ethnicities, career experiences, and ways of thinking have, as a result, a more diverse and aware mind-set.”

Goldman’s new policy contrasts sharply with how the bank has done business in the past: In 2017, 55 percent of the companies it had underwritten had no women on their boards, according to 2020 Women on Boards research. And as recently as 2019, the bank argued that it would simply let investors decide if they liked a company’s board.

Private equity firms are also pushing their portfolios of smaller firms to diversify their boards, even if they don’t have any imminent plans for an initial public offering.

TheBoardlist, an online platform that has curated and vetted thousands of female director candidates and connected them with companies, noticed an uptick in demand for female directors for both public and private companies immediately after the California legislation passed, Shannon Gordon, the chief executive, said. It was an indication that companies are quietly beginning to evaluate their diversity efforts regardless of public scrutiny.