There are many wonderful things about being a mom, and we’ll celebrate them on Sunday. But there’s one awful thing, too: There’s a severe financial penalty for becoming a mother in the United States.

Mothers make 73 cents, on average, for every dollar fathers make, according to an analysis of Census data released by the National Women’s Law Center earlier this week. If you look only at African-American mothers, it’s worse: 53 cents for every dollar a white, non-Hispanic dad makes. For Latinas, it’s 47 cents, less than half what white fathers earn.

The motherhood wage gap is even wider than the one faced by women overall -- 79 cents on the dollar.

The good news is there’s an existing public policy that, if expanded, could help fix this: public school.

Extending the school day and making school a year-round thing would bring much-needed help to the country’s working parents and help reduce the wage penalty faced by women, Claudia Goldin, an economist at Harvard and one of the leading researchers on the wage gap, told The Huffington Post earlier this year. It’s a proposal she also floated in a terrific interview about the wage gap she did on the “Freakonomics” podcast.

“We have a policy that says every child is guaranteed a public school education in the United States. No one ever said that school started at 5 years old or stopped in June or stopped at 2:30 in the afternoon,” Goldin said. “There’s nothing more killing for parents, or women in particular, than having a child that gets out of school at 2:30.”

Looking at it this way, it’s easier to balance work and parenting responsibilities, if you have a 2-year-old, Goldin said. Daycare doesn’t end at 2:00 in the afternoon.

People without kids might not intuitively understand what a game changer this would be. One of the biggest reasons moms don’t make as much money as fathers is that mothers can’t work the same kinds of hours as fathers (generally speaking). The burden often falls on them to be around when kids get out of school or juggle some kind of after-school child care arrangement.

A woman might take a job with more flexibility and less-demanding hours in order to be available during the times the kids are out of school, Goldin said. That job will typically pay less. This is the reason that the gender wage gap is widest for the highest earners.

Women at the top make 84 percent of what men at that level earn after controlling for education, ethnicity and a few other factors, revealed a working paper released this year by two well-regarded labor economists.

Women at this level step away from the kinds of jobs that pay the most because they require too many hours of work, Goldin said. I'm talking about fancy six-figure jobs at elite law firms, consulting firms, or high-level C-suite positions.

That does not mean that women “choose” to make less money, Goldin was careful to say. “They’re purchasing amenities.” Women are paying for flexibility and time.

They’re paying a lot.

Of course, there are other reasons mothers make less than fathers. Discrimination plays a big role. Mothers face a wage penalty -- making 5 percent less for each child they have, according to one study. Men do not face a similar fatherhood penalty, often making more money after becoming a dad, the same study notes. Employers consciously or unconsciously believe mothers are less devoted to work.

There are many who advocate fixing the wage gap through company benefits -- have employers offer more flexibility to workers. This way, women stick around longer and advance to higher-paying positions. But these kinds of work policies can often backfire, Goldin said, as employers would avoid hiring women, believing that they would spend more time away from the office. Some jobs don't allow for more flexibility, for that matter.

A longer school day wouldn't bump up against those issues.

The best way to help close the wage gap is to expand an already existing policy, Goldin said. “Who could argue with that?”