IRVING, Texas — Crowded around a workshop table, four girls at de Zavala Middle School puzzled over a Lego machine they had built. As they flashed a purple card in front of a light sensor, nothing happened. 

The teacher at the Dallas-area school had emphasized that in the building process, there are no such thing as mistakes. Only iterations. So the girls dug back into the box of blocks and pulled out an orange card. They held it over the sensor and the machine kicked into motion. 

“Oh! Oh, it reacts differently to different colors,” said sixth grader Sofia Cruz.

In de Zavala’s first year as a choice school focused on science, technology, engineering and math, the school recruited a sixth grade class that’s half girls. School leaders are hoping the girls will stick with STEM fields. In de Zavala’s higher grades — whose students joined before it was a STEM school — some elective STEM classes have just one girl enrolled. 

Efforts to close the gap between boys and girls in STEM classes are picking up after losing steam nationwide during the chaos of the Covid pandemic. Schools have extensive work ahead to make up for the ground girls lost, in both interest and performance.

In the years leading up to the pandemic, the gender gap nearly closed. But within a few years, girls lost all the ground they had gained in math test scores over the previous decade, according to an Associated Press analysis. While boys’ scores also suffered during Covid, they have recovered faster than girls, widening the gender gap.

As learning went online, special programs to engage girls lapsed — and schools were slow to restart them. Zoom school also emphasized rote learning, a technique based on repetition that some experts believe may favor boys, instead of teaching students to solve problems in different ways, which may benefit girls. 

Old practices and biases likely reemerged during the pandemic, said Michelle Stie, a vice president at the National Math and Science Initiative.

“Let’s just call it what it is,” Stie said. “When society is disrupted, you fall back into bad patterns.”

Related: A lot goes on in classrooms from kindergarten to high school. Keep up with our free weekly newsletter on K-12 education.

In most school districts in the 2008-09 school year, boys had higher average math scores on standardized tests than girls, according to AP’s analysis, which looked at scores across 15 years in over 5,000 school districts. It was based on average test scores for third through eighth graders in 33 states, compiled by the Educational Opportunity Project at Stanford University. 

A decade later, girls had not only caught up, they were ahead: Slightly more than half of districts had higher math averages for girls.

Within a few years of the pandemic, the parity disappeared. In 2023-24, boys on average outscored girls in math in nearly 9 out of 10 districts.

A separate study by NWEA, an education research company, found gaps between boys and girls in science and math on national assessments went from being practically non-existent in 2019 to favoring boys around 2022.

Studies have indicated girls reported higher levels of anxiety and depression during the pandemic, plus more caretaking burdens than boys, but the dip in academic performance did not appear outside STEM. Girls outperformed boys in reading in nearly every district nationwide before the pandemic and continued to do so afterward.

“It wasn’t something like Covid happened and girls just fell apart,” said Megan Kuhfeld, one of the authors of the NWEA study. 

Related: These districts are bucking the national math slump 

In the years leading up to the pandemic, teaching practices shifted to deemphasize speed, competition and rote memorization. Through new curriculum standards, schools moved toward research-backed methods that emphasized how to think flexibly to solve problems and how to tackle numeric problems conceptually.

Educators also promoted participation in STEM subjects and programs that boosted girls’ confidence, including extracurriculars that emphasized hands-on learning and connected abstract concepts to real-life applications. 

When STEM courses had large male enrollment, Superintendent Kenny Rodrequez noticed girls losing interest as boys dominated classroom discussions at his schools in Grandview C-4 District outside Kansas City. Girls were significantly more engaged after the district moved some of its introductory hands-on STEM curriculum to the lower grade levels and balanced classes by gender, he said.

When schools closed for the pandemic, the district had to focus on making remote learning work. When in-person classes resumed, some of the teachers had left, and new ones had to be trained in the curriculum, Rodrequez said. 

“Whenever there’s crisis, we go back to what we knew,” Rodrequez said. 

Related: One state tried algebra for all eighth graders. It hasn’t gone well

Despite shifts in societal perceptions, a bias against girls persists in science and math subjects, according to teachers, administrators and advocates. It becomes a message girls can internalize about their own abilities, they say, even at a very young age. 

In his third grade classroom in Washington, D.C., teacher Raphael Bonhomme starts the year with an exercise where students break down what makes up their identity. Rarely do the girls describe themselves as good at math. Already, some say they are “not a math person.” 

“I’m like, you’re 8 years old,” he said. “What are you talking about, ‘I’m not a math person?’” 

Girls also may have been more sensitive to changes in instructional methods spurred by the pandemic, said Janine Remillard, a math education professor at the University of Pennsylvania. Research has found girls tend to prefer learning things that are connected to real-life examples, while boys generally do better in a competitive environment. 

“What teachers told me during Covid is the first thing to go were all of these sense-making processes,” she said. 

Related: OPINION: Everyone can be a math person but first we have to make math instruction more inclusive 

At de Zavala Middle School in Irving, the STEM program is part of a push that aims to build curiosity, resilience and problem-solving across subjects.

Coming out of the pandemic, Irving schools had to make a renewed investment in training for teachers, said Erin O’Connor, a STEM and innovation specialist there.

The district last year also piloted a new science curriculum from Lego Education. The lesson involving the machine at de Zavala, for example, had students learn about kinetic energy. Fifth graders learned about genetics by building dinosaurs and their offspring with Lego blocks, identifying shared traits. 

“It is just rebuilding the culture of, we want to build critical thinkers and problem solvers,” O’Connor said.

Teacher Tenisha Willis recently led second graders at Irving’s Townley Elementary School through building a machine that would push blocks into a container. She knelt next to three girls who were struggling.

They tried to add a plank to the wheeled body of the machine, but the blocks didn’t move enough. One girl grew frustrated, but Willis was patient. She asked what else they could try, whether they could flip some parts around. The girls ran the machine again. This time, it worked.

“Sometimes we can’t give up,” Willis said. “Sometimes we already have a solution. We just have to adjust it a little bit.” 

Lurye reported from Philadelphia. Todd Feathers contributed reporting from New York. 

The Associated Press’ education coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org.