New research indicates that while the gender pay gap has been closing for decades, progress has nearly stalled since the mid-1990s — and women aren't benefiting from the incremental improvements.

That's according to a working paper by Jaime Arellano-Bover from the Yale School of Management, Nicola Bianchi from Northwestern University, Salvatore Lattanzio of the Bank of Italy and Matteo Paradisi of the Einaudi Institute for Economics and Finance.

Women on average are paid 84 cents for every dollar paid to by men, according to an analysis of U.S. Census Bureau data by the National Women's Law Center. That's not much better from 2002 data when women were paid roughly 80% as much as men.

The researchers analyzed more than 40 years of pay data from the Census Bureau's current population survey to determine what's behind the persistent gap, and what could fuel equity moving forward.

In the '70s, Arellano-Bover tells CNBC Make It, two patterns drove the closing of the wage gap: Young men and women were entering the workforce being paid similar wages, and older workers (who tend to have wider wage gaps that have compounded over time) were retiring from the labor force.

"So between the mid-'70s and the mid-'90s, we had these two forces that both helped push down the aggregate gender pay gap, and newer cohorts were progressively more-gender equal in terms of their outcomes," Arellano-Bover says.

However, by the late '90s and early 2000s, the pay gap among young workers stopped narrowing. Meanwhile, the research suggests that the retirement of older workers with wider gaps is the sole contributor to decreasing the gender pay gap overall.

The study's findings challenge the assumptions that the narrowing gender pay gap is the result of better career opportunities for women, Arellano-Bover says. Rather, the narrowing gap could indicate poorer wage and career opportunities for men.

Looking at the average wage distribution of 25-year-olds over the years, researchers found that "young men were falling in wage distribution rather than young women going up," Arellano-Bover explains. In other words, "young women have done a tiny bit better between the mid-'70s and mid-'90s, but that how much better they have done is very small relative to how much young men have dropped in the wage distribution."

Pay equity starts with educational opportunities

It's troubling that the wage gap for young workers hasn't improved given that early-career gaps have long-term consequences, Arellano-Bover says. As a result, the authors suggest that policies to close the wage gap should focus on early-career interventions for young women entering the job market.

"If one is striving for gender equality in the labor market, it's important to tackle disparities when young people enter the labor market — or even before, when young people are deciding what to study," Arellano-Bover says.

Equity-focused policies could start as early as grade school when students develop interests in what they want to study in college or consider what their future careers might be.

For example, previous research has shown that while similar shares of Gen Z boys and girls say they get opportunities to learn about STEM in school, girls are more likely to say they're not interested in the topics or think they'll be bad at it.

The discrepancy may come down to how girls feel they'll be perceived for trying something they have no experience doing, compared with a perhaps "irrational confidence young men have in things they've never done before," says Zach Hrynowski, a senior education researcher with Gallup.

Further, girls are more likely than boys to say STEM careers "are not accepting of people like me." 

When young women don't pursue high-paying fields like in STEM, it can have lifelong impacts on their earnings.

Even though more women than men are graduating from college, "men are much more likely to study majors that lead to high-paying jobs than young women," Arellano-Bover says, "and this gap in major choice has been very flat for the last 20 to 30 years" as the wage gap has persisted.

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