Nearly half a century after a federal law barred gender discrimination at schools and universities, blatant inequities remain, with girls and women routinely cheated out of academic and athletic opportunities, research shows.

The inequities leave girls at a disadvantage on playing fields and in life.

Oakland Unified School District recently offered an extreme example when it eliminated sports programs to save money, ignoring a disproportionate impact on girls, according to civil rights attorneys.

Across California, 819,625 students participated in competitive sports last school year — 57 percent were boys and 43 percent girls, even though enrollment is nearly equal, the National Federation of State High School Associations reported in its annual survey. A legal advocacy group found that less than half of California school districts are complying with a state law requiring them to report gender participation in sports.

“The public does not seem to have that grasp, nor do the schools, that it is a systemic problem,” said Amy Poyer, senior staff attorney at the California Women’s Law Center. Girls are “just so used to being pushed to the side.”

The Oakland district’s decision to cut 10 high school competitive sports, announced Aug. 24, affected twice as many girls as boys, which represented a clear violation of federal Title IX law against sex discrimination in schools, the legal experts said.

“It was so clear that it never occurred to them to consider the gender inequity,” said Elizabeth Kristen, director of gender equity at Legal Aid at Work. “What an absolutely terrible message to send to girls: ‘You don’t matter.’”

On Friday, Oakland officials offered a more complete explanation for the cuts, saying the decision was made in a rush to balance the budget and without adequate staffing.

“This was a mistake that we made on multiple levels, due in large part to the high turnover rate here at OUSD,” said district spokesman John Sasaki. “We have had people come and go in leadership at the district and at the Oakland Athletic League, including recently. ... That being said, there is a need for additional training on Title IX across the organization.”

Since the cuts were announced, Kristen said she has been working with at least two Oakland families interested in suing the district over inequities in the athletic programs. She plans to file a demand letter, putting the district on formal notice of potential litigation.

While community donations in the past week helped save some of the sports, the lapse spurred parents and lawyers to take a closer look at the district, where participation in sports skewed in favor of boys even before the cuts.

“I still feel like what it did was it just shined a light on an existing problem,” Kristen said. “Even if you restore (the sports) they had, they still have a problem.”

Less than 46 percent of Oakland students who played competitive sports this past school year were girls, even though females made up about 49 percent of student enrollment, according to the California Interscholastic Federation.

At some schools in the district, however, inequity is more stark. At Castlemont High, girls made up 44 percent of enrollment, but only 35 percent of student athletes, according to 2016-17 data, the most recent information available.

Experts on Title IX say that while Oakland’s disregard for gender equity in making the cuts to sports was baffling and stunning, similar participation gaps are common across California schools, illustrating an ongoing issue with offering girls equal opportunity in athletics.

“I don’t think schools are discriminating on purpose, but they’re still discriminating based on these large gaps,” Poyer said. “There are still such huge disparities.”

Fighting the problem can mean filing lawsuits school by school, demonstrating inequities in participation, facilities, resources, uniforms and prime practice times, Poyer added.

“It feels like an overwhelming mountain to climb,” she said.

Oakland officials are reviewing data to determine where gaps remain and plan to hold training sessions for school administrators, district staff and athletic directors to ensure Title IX compliance, Sasaki said.

To help expose gender inequities in sports, the state passed a law four years ago requiring each public K-12 school to post annual reports detailing total enrollment, number of athletic teams and participation in competitive sports by gender, starting with the 2015-16 school year.

A random sampling of schools in 2017 found that less than half in the state were posting the data as required, according to a report by Fair Play for Girls in Sports, a Legal Aid for Work project. Oakland is among those failing to fully comply with the state law.

District officials were working to complete the past-due reports and update 2017-18 numbers and reviewing participation rates of male and female athletes “to see where we need to increase athletic participation,” Sasaki said.

Among schools posting participation numbers, the statewide report found an average six-percentage-point gap between the number of girls enrolled and the number playing a sport.

Across California, that translates to more than 100,000 girls.

Nationwide, that participation gap means 1.2 million fewer chances for girls to play sports in high school, according to the National Women’s Law Center.

The impact on girls later in life is tangible, according to the center. Studies link being a high school athlete to 14 percent higher wages for women. And of 400 female executives surveyed, 94 percent played organized sports growing up.

“I feel like it’s really dollars and cents for girls that they’re being deprived of,” Kristen said.

About 30 miles south of Oakland, Fremont Unified is among the districts regularly posting sports participation data and keeping tabs on Title IX requirements. Girls in the district make up 48 percent of high school enrollment but 45 percent of those participating in competitive sports.

It’s something that requires consistent monitoring to ensure girls have the same opportunity to participate in academics and athletics, said Raul Zamora, assistant superintendent of human resources and the district’s Title IX coordinator.

“We’re trying every day to move forward with what needs to happen,” he said, acknowledging there is still work to do to eliminate gaps.

Zamora gave a recent example of a few elementary schools that decided to start an after-school basketball program and had to be reminded to make sure girls were playing, too.

It couldn’t just be boys’ teams, he said.

“Not going to happen,” he said. “At least not under my watch.”

Jill Tucker is a San Francisco Chronicle staff writer. Email: jtucker@sfchronicle.com Twitter: @jilltucker