ASHLAND CITY, Tenn.— Delainey Tidwell says she loves reading. The tricky part for her is understanding the words on the page.

“I would read one sentence over and over again,” said the 9-year-old fourth-grader.

Though she returned to school in August 2020, repeated quarantines left her mostly on her own at home. Her father is a construction supervisor who has to be on site. Her mother works from home but gets few breaks during the day. Delainey sometimes had to care for her little sister during virtual school.

Delainey’s difficulty with comprehension is also hurting her in math class, where she struggles to understand word problems, said her mother, Danyal Tidwell, who pins some blame on the pandemic. “We want to give her every resource we can between school and home, because we want her caught up,” Mrs. Tidwell said.

For two years, schools and researchers have wrestled with pandemic-era learning setbacks resulting mostly from a lack of in-person classes. They are struggling to combat the learning loss, as well as to measure just how deep it is. Some answers to the second question are becoming clear. National data show that children who were learning to read earlier in the pandemic have the lowest reading proficiency rates in about 20 years.

The U.S. Department of Education last Thursday released data showing that from 2020 to 2022, average reading scores for 9-year-olds slid 5 points—to 215 out of a possible 500—in the sharpest decline since 1990. Average math scores fell 7 points to 234, the first statistically significant decline in math scores since the long-term trend assessments began in the 1970s.

Learning loss generally is worse in districts that kept classes remote longer, with the effects most pronounced in high-poverty districts, researchers say. Yet reading scores are below 2019 levels for certain grades even in some states that quickly returned to in-person instruction, such as Florida.

Among possible reasons, educators say, are that some students stayed remote after in-person classes resumed, Covid-19 outbreaks led to additional quarantining and class routines were disturbed by practices such as social distancing.

While some students have begun to make up ground, researchers say that, on average, it could take five years or more for today’s fourth-graders to read proficiently unless the pace accelerates. By then, billions of dollars in federal pandemic-related aid for education will have run out.

These students are at a pivotal stage. Educators pay particular attention to 9-year-olds’ literacy rates because research shows that reading ability by the end of third grade can be predictive of educational success, career earnings and the risk of incarceration. A study released in 2011 by the Annie E. Casey Foundation found that 16% of students who don’t read proficiently in third grade fail to graduate from high school on time, a rate four times that of proficient readers.

“If students are not reading at grade level, then what does it mean for the content they’re taking in in their other subjects? Are they not as prepared to be able to participate in their math classes and their social studies classes?” said Karyn Lewis, director of the Center for School and Student Progress at NWEA, a nonprofit research firm that has studied how long it may take for proficiency rates on its tests to rebound.

Susan Collins tutors 9-year-olds at East Cheatham Elementary School in Ashland City, Tenn. Left to right are Olivia Hogan, Delainey Tidwell and Riley Brooks.

State education leaders were acutely aware of the stakes well before Thursday’s data from the National Assessment of Educational Progress, and are pumping billions of dollars into hoped-for solutions, from small-group tutoring to expanded summer school, and aiming to offer students more individual attention.

In some cases, the efforts coincide with incremental improvements for struggling students, but educators say they won’t know for years whether their efforts are a match for a problem this big.

“Without any prior experience as a guide, practitioners are sort of winging it—providing tutors to some students, double-dose math and summer school to others—and then just hoping that it all adds up to enough,” said Thomas Kane, an economist and professor of education at the Harvard Graduate School of Education.

A concern, he said, is that districts might apply solutions and discover their inadequacy only after the federal aid is spent. The biggest pandemic relief program, the American Rescue Plan, earmarked $122 billion for K-12 public schools and required that at least 20% go toward addressing learning loss. In many districts it should be close to 100%, in Prof. Kane’s view.

State-level test results show reading scores still largely below prepandemic levels. In Indiana, the legislature last year approved a $150 million grant program for organizations, such as the United Way, that are offering in-person programs with extended learning time.

Indiana also offers families up to $1,000 to enroll in private tutoring. The program, largely bankrolled by federal aid, targets students who qualify for free or reduced-cost lunches and who were below proficiency in both English language arts and math in the third or fourth grade.

“We have to acknowledge that some of the things that we’re going to deploy in terms of initiatives are going to be very, very successful. Some might just help us stabilize. Some might not work as they were intended,” said Indiana Education Secretary Katie Jenner. The state has begun analyzing its return on investment, but that will take time, she said.

An office that North Carolina formed last year is leading efforts to assess learning-loss initiatives. The state’s Office of Learning Recovery and Acceleration has found that a summer-school program that enrolled 250,000 students in 2021 had a small but positive impact on math and reading scores.

A page of a 4th-grade student workbook at Charlotte Park Elementary in Nashville.

The office is working with a University of North Carolina at Chapel Hill research center to launch studies of learning-loss programs, said Michael Maher, who heads the office. Despite the urgency to fund programs, “we still have to be mindful of how we’re going to spend this money,” Dr. Maher said.

Texas is a rare example of a state where young students’ reading scores have more than bounced back to prepandemic levels. In 2022, half of Texas third-graders met or exceeded expectations, up from 37% in 2021 and 43% in 2019, according to state data.

A key part of the learning-loss recovery effort in Texas is a measure passed by the legislature in 2021 that provides 30 hours of tutoring for students on the subject matter of each test where they failed to meet grade level.

Tennessee is among a handful of states that have taken aggressive action and managed to lift statewide results above 2021 levels, though still not back to scores before the pandemic for some subjects or grade levels. Tennessee’s spring 2022 assessment of English language arts scores for third-graders showed 36% were proficient, which was up from 32% in 2021 but still slightly behind the 37% in 2019.

State Education Commissioner Penny Schwinn calls the 2019 baseline unacceptably low. “We grew five to seven points, depending on the grade level, this year. That needs to happen every year for a number of years for our state to be where we know it can be,” she said. “We can’t have reading be less than a flip of a coin whether or not your child’s on grade level.”

One Tennessee effort involves instructing teachers in the science behind learning to read. More than 18,000 teachers have completed 60 hours of instruction, which includes strategies to help struggling readers.

In Nashville, fourth-grade teacher Makayla Walker is gearing up to start tutoring some of her students after school as part of Tennessee’s tutoring program, which began in the 2021-22 school year. Over three years, the program is expected to reach 150,000 students, underwritten by $200 million in federal aid. The state is investing $170 million in that program as well as a summer learning camp initiative created in response to the pandemic.

Teacher Makayla Walker in her classroom at Charlotte Park Elementary.

The tutoring is high-dosage, meaning students meet two or three times a week for 30 or 45 minutes, for at least a semester. The groups are small, three students per tutor in elementary school. The program is designed for students who are approaching proficiency and need a boost.

“I think it could make a world of difference,” Ms. Walker said. “Because I am their general education teacher, I already kind of have an idea of how they need support in here. So it will really allow me to build on that.”

Last school year the Nashville district tutored 745 third-graders in literacy and more than 3,000 students overall. The district said it is working with Brown University to study the effectiveness. Summer learning participants in 2021 showed slightly higher reading gains than students who didn’t take part, officials said.

Across Metro Nashville Public Schools, about 27% of third-graders tested proficient in English language arts on 2022 state assessments. That was a 5-point jump from 2021 and put the district near its 29% rate of 2019.

Assessment scores at Ms. Walker’s school, Charlotte Park Elementary, where many students come from low-income families, are lower than the district’s. Of the 16 children in her classroom on a recent day, just four or five read at grade level, she said. An added challenge: For 11 of her students, many of them Hispanic, English isn’t their first language.

Even after students could return in person, many stayed remote, and others are still adjusting to being back in class, she said. That requires “more consistent redirection or reconnection with what we’re doing, and I find that that is what’s preventing some of them from attaining the skills that are missing,” she said.

Ms. Walker, who uses a high-octane call-and-response method to engage her students, pulled three children aside on a recent day for extra reading instruction at a table in a corner of her classroom.

She had each child write the word ”tap” and sound out each letter. Then she had them add “e” to make “tape.” They repeated the exercise with “pin” and “pine.”

“The “e” is what?” she asked.

“Silent,” replied one of the students.

Ms. Walker said she has no illusions she can erase huge learning gaps in one year. “But do I think that I can help them meet personal goals for themselves based on our testing? Yeah, I do,” she said. “I think that it takes a partnership at this age with the kids. I think that they should be held accountable for their learning.”

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About 20 miles to the northwest, the Tidwells jumped at the chance for their daughter, Delainey, to work with a reading tutor this school year at East Cheatham Elementary, where many students are from poorer households.

Tutor Susan Collins greeted Delainey and two other fourth-grade girls for their first 45-minute session on a recent morning. They sat around a table in a conference room, beneath a framed print that read “be kind.”

Susan Collins at a tutoring session at East Cheatham Elementary in Ashland City.

The school district in rural Cheatham County was an early adopter of the state’s tutoring program, with math the focus last year. Third-graders’ proficiency rate in English language arts was 40% in 2022, the highest in at least four years but still far too low, said Cathy Beck, the district’s director of schools.

Mrs. Collins, a teacher with 32 years of experience and a warm manner, taught the three girls what “plethora” means, discussed prepositional phrases and shared stories about her own love of reading.

The girls took turns relating their reading challenges. Delainey spoke of her difficulty with comprehension. Riley Brooks said she wants to read faster. Olivia Hogan said she often skips a word or sentence, adding, “I think I can get better.”

Mrs. Collins promised them they would all get better in the months to come.

“Not only are you going to learn everything there is about reading,” she said, “you’re going to learn everything I can teach you—in two days a week—about writing.”

Write to Scott Calvert at scott.calvert@wsj.com