Free public school starting at age four, or even three, is growing in many American cities. It's gaining traction as a way to help young children learn the reading, counting and social skills that prepare them for kindergarten. It also promises to help close academic gaps between rich and poor children. Above all, it may have lasting benefits for attendees, including success in school and better lives as adults.

But promises are not guarantees, and universal pre-K works better in some places than in others. Washington, D.C., runs one of the country's oldest, best-funded, most comprehensive pre-K systems. So what can other cities learn from Washington's success?

Here's how pre-K looks in one Washington classroom:

Amina, who is 4 years old and introduces herself as a writer, looks up from chopping plastic carrots. She and two of her classmates are pretending to cook a family meal together. Her "sister" Lesley, who said she is a librarian-professor, is prepping tomatoes. Their third "sister," Madison — "I don't work. I just sit on my computer all day," she said — is making caramel for the salad. That doesn't seem right, I say.

Amina shrugs. It's an odd salad, but not out of bounds for the dramatic play center at the Parklands campus of AppleTree Early Learning Public Charter School. It's in the Shipley Terrace neighborhood of Washington, a largely low-income, African-American part of the city.

Amina gathers all the ingredients and passes me the bowl. "Here! Try some!"

Amina, Lesley and Madison are three of the more than 13,000children enrolled in Washington's universal public pre-K program.

The city introduced universal pre-K in 2008. Over the next decade, glittering rhetoric about pre-K's benefits helped sell the public — and policymakers across the country — on the idea. Studies show that high-quality pre-K can advance children's linguistic, academic and social development. Research also suggests that pre-K programs reduce the need for special education placements, raise students' future incomes, lower incarceration rates and get parents back to work.

And yet enthusiasm for these programs has often outrun practicalities. Several studies of recent efforts to increase public pre-K have hinted that cities and states have expanded access at the cost of quality. Some expansions have been rushed and others given too little money; many face both problems.

Beside issues of politics, there are questions of what we want universal pre-K to do. "The big problem in the sector is, what do we mean by quality?" asks Jack McCarthy, AppleTree's president and chief executive.

The range of pre-K's promised benefits makes this a surprisingly complex question. Is the goal academic readiness, social and emotional learning, better health outcomes, access to child care, raising future incomes, decreasing the size of future prison populations — or some combination of these? Then, once we've defined success, how do we measure it? And, finally, how can new pre-K programs in cities like New York, San Antonio and Seattle deliver it?

A decade into building — and reforming — its universal pre-K program, Washington provides some hints.

The program is popular with parents: 73 percent of 3-year-olds and 85 percent of 4-year-olds were enrolled in the 2017-2018 school year. "With the pre-K participation rates that we have across the city, I think we can truly say that our public education system starts at age three," says Miriam Calderon, who was the school district's director of early childhood education during the program's early years. (Now she heads Oregon's early education system.)

The city's enthusiasm for early education is at least partly a function of its skyrocketing cost of living. Washington designed its pre-K program to help families financially and became one of the few cities that offers it to 3-year-olds, leaving new parents with just three years of child care to cover.

It also runs all day. Most campuses provide at least six and a half hours of care and education each day. A Center for American Progress study found that Washington's program has increased mothers' participation in the labor force.

But quality pre-K isn't solely — or even primarily — about helping parents afford to have children or get back to work. Analysis of universal early education programs like Quebec's suggest that while it is reasonably straightforward to provide safe, daylong care that allows parents to return to work, it is more complicated to ensure that these programs also advance children's development.

Across Washington, educators and administrators say that pre-K classrooms aim to close academic achievement gaps before they have grown too large. Such measurement makes sense: Just as second grade prepares children for third and middle school prepares children for high school, pre-K ought to pre-prepare children for kindergarten.

Of course, kindergarten preparation is unique. It covers a holistic span of child development, and it's long on social and emotional skills — paying attention, working with peers, recognizing and solving conflicts. It's about learning how to be at school and how to get the most out of it. For instance, when Amina, Lesley and Madison serve caramel salad, they're learning to create collaboratively in a team.

Laura Steinmetz, a pre-K teacher in Washington, calls this "the underlying piece" of her work. Take wooden blocks. They develop some obvious skills: Students acquire dexterity and learn how their choices affect a structure's stability. They learn to plan and persist in the face of failure. But there's more, Ms. Steinmetz says. "Maybe somebody walked by and touched one of the support blocks and the whole thing fell down, so you have to learn how to manage your feelings and talk to that peer."

Turner Elementary School's principal, Eric Bethel, said he's seeing the impact of the pre-K program in his kindergartners. "They're not spending the first three or four weeks of school crying because it's some sort of foreign place to them," he said. "They know school routines. They have stamina."

But high-quality pre-K isn't only about patiently navigating imaginary salads, block towers and frustration. These social and emotional skills help students' acquire knowledge by building their abilities to learn in group settings. Good pre-K also builds academic foundations.

At a literacy table in one Turner classroom, Tanisha Watson, a veteran pre-K teacher, reads "Be Boy Buzz" with a student. The boy prompts her to read by pointing to each word. In just two minutes, she reinforces a pile of basic literacy skills. "If I read, you'll point, right? Are you ready? We go left to right," she reminds him. "Do we start at the bottom or the top? What's that period mean? O.K.! Now we need to keep going. What do we do to keep reading? We turn the page? Great!" She stretches him to think about what's happening — "Does he seem like he's talking loud? What do you think he's doing here? He's crying? How do you know? Why is he crying?" Those are the building blocks of reading.

Skilled instruction like Ms. Watson's doesn't come cheap. Unlike most American communities, Washington pays its pre-K teachers at rates similar to those its elementary schoolteachers get. Their salaries make up a large part of the nearly $19,000 the city spends annually on each preschooler. San Antonio, for comparison, spends just under $14,000 per child.

What's more, Washington also uses federal Head Start funding in its pre-K sites. All district pre-K classrooms must adopt Head Start's holistic approach to child development, which means providing access to health, nutrition and family outreach programs. In many cities, public pre-K classrooms enroll students separately from Head Start classrooms, which primarily serve children from low-income families. Washington's systemwide funding coordination helps avoid this de facto segregation. No other city blends local and federal early education funding as smoothly on a large scale.

Most important, more than 95 percent of Washington's pre-K seatsare in public schools. This can help students acclimate to the facilities where they'll spend their elementary school years. It can also make it easier for kindergarten to pick up precisely where pre-K leaves off.

Just five years ago, 80 percent of kindergartners at Turner Elementary started the year behind on basic print concepts, like how to hold and use a book. As the school's pre-K program has improved — Turner's pre-K teachers have worked with a full-time coach for three years — the data have flipped. Last year, 76 percent of incoming kindergartners had mastered those reading basics.

At both Turner Elementary and AppleTree's Parklands campus, nearly every student is growing up in a low-income, African-American family. But Washington's pre-K classrooms seem to be getting results with all their students.

For example, children who were learning English at schools using AppleTree's curriculum finished pre-K performing as well as, or better than, native English-speaking peers on math and literacy tests. At AppleTree's Columbia Heights campus, children who speak a language other than English at home — one-third of the school's students — showed stronger growth on early literacy and math skills than their native English-speaking peers.

In 2018, the school district reported that fewer than half of 3-year-olds were meeting early literacy benchmarks when they arrived in pre-K classrooms. However, 86 percent were finishing pre-K ready for kindergarten on the cognition skills measured by the city's early childhood assessment — and 83 percent were becoming kindergarten-ready on language metrics. More than 75 percent reached kindergarten-ready skills on fluently matching sounds with letters.

It is too early to say for certain whether Washington's system is delivering on all of the many promises made on pre-K's behalf. (Paradoxically, the program's popularity makes it difficult to study, because there are few students outside the program who could make up a control group.) Right now, the earliest 3-year-olds to have enrolled in the city's expanded pre-K system are only now arriving in the later elementary grades, where standardized academic assessments become more common. Students in Washington's public schools have shown steady academic improvement on the National Assessment of Educational Progress, particularly in the elementary school years. While many factors contribute to this trend — the city simultaneously embarked upon major K-12 education reforms and has seen significant demographic changes in its schools — these are grades that enroll more students who attended the city's pre-K programs.

But it will be decades before researchers can determine whether the program has affected students' incomes or incarceration rates as adults. So far, though, Washington's example does suggest that a universal, full-day, well-funded, school-based, developmentally-appropriate, holistic pre-K program can improve children's lives — if the public is patient, and willing to pay.

Conor P. Williams (@ConorPWilliams) studies educational equity as a fellow at the Century Foundation.

PSAGOT, West Bank — The fun was over before the tour bus rolled into Har Gilo.

For the past week, 28 college students from the United States had been taking part in a traveling experiment billed as an alternative to Birthright Israel, whose free trips to the country have become a rite of passage for hundreds of thousands of young American Jews.

Birthright's avoidance of the Israeli occupation of the West Bank has made it the target of angry protests by left-leaning Jewish activists. But for sheer ambition, no critique has approached this week's attempt by the liberal lobbying group J Street to map out an alternative route for Birthright's tours.

The organizers said they embraced Birthright's goal of helping young American Jews connect with Israel and with their Jewishness, but that they also needed to be exposed to the realities of the occupation.

On Sunday, after several upbeat days hiking in the Galilee, learning about the kibbutz movement and bonding over buffets and Israeli pop songs, the J Street cohort took a sharp left turn into territory where Birthright does not go.

In the West Bank settlement of Har Gilo, they received a harsh history lesson from a veteran opponent of the occupation. Then they toured an impoverished, water-starved Palestinian village that Israeli settlers want to demolish, and visited the city of Hebron, where repeated outbreaks of violence have turned an entire Palestinian business district into a ghost town.

Adam DeSchriver, 21, a clarinet student at the Eastman School of Music in Rochester, N.Y., said he had been wowed on the trip's first few days by the "renaissance of Hebrew culture" he discovered in Israel.

"What breaks my heart," he said after Sunday's eye-opening itinerary, "is seeing it at the expense of others."

Birthright officials say their trips do address the Israeli-Palestinian conflict to a limited extent, but that it is not their focus.

Birthright's goal is "to strengthen Jewish identity and foster a love for the land, people and culture of Israel," said Pamela Fertel Weinstein, a spokeswoman for the group. Travelers more interested in the conflict, she said, are free to stay on in Israel to learn about it on their own.

The organizers of the J Street trip, called "Let Our People Know," said newcomers to Israel also needed to understand the experiences of Palestinians living under Israeli occupation.

"To be raising a generation of American Jews with no knowledge of that? That's wrong," said Shira Wolkenfeld, 22, a new graduate of George Washington University and a member of J Street's student board. "And that's political. We're creating a generation who don't have the knowledge to speak out against it."

The ride to Har Gilo, just south of Jerusalem, took the bus through an Israeli checkpoint. Hagit Ofran, a leader of Peace Now, addressed the group over a microphone and described how soldiers decided which motorists to stop: "To look suspicious," she said, "you need to look Arab."

It was a bracing how-do-you-do for liberals unaccustomed to blunt racial profiling.

But it was atop Har Gilo, peering out over the southern West Bank, that the travelers began to see troubling aspects of a country they had mainly loved from far away.

Down below was the separation barrier, with decorous brickwork beautifying the side facing an Israeli settlement. The Palestinian village on the other side looked upon a crude concrete slab.

Farther downhill was the tunnel road, a bypass highway to speed Israelis to and from their growing settlements, tunneling under Palestinian villages and surfacing between high concrete walls to protect Jewish drivers from potential attacks by Palestinians.

"You don't feel the occupation when you don't see it," Ms. Ofran said.

She was referring to the drivers in the distance, but she could have been referring to the young passengers who climbed back onto their tour bus.

Nasser Nawajah, a Susiya resident and activist with the Israeli human rights group B'Tselem, told Susiya's story: Evicted from their old homes just downhill to make way for an Israeli archaeological site, Susiya's shepherds had set up a ramshackle collection of tents and huts here in their fields, lest their grazing lands be taken from them as well.

An organization of Jewish settlers has sued to compel the army to demolish Susiya, since the tents and huts were built without permits — permits that Israel does not grant to Palestinians across much of the West Bank.

Susiya's residents were also cut off from their cisterns and barred from digging new ones, Mr. Nawajah said. They asked Israel's water company, which has a big line just across the street, to install a spigot and a meter so they could pay for water for their families and sheep. It said no, because the village was built illegally. So the villagers truck in water, he said, paying many times what it costs Israelis to drink and bathe.

"How do you fight back?" one of the young visitors asked. International pressure is the only thing that works, Mr. Nawajah said.

"Is there anything we can do?" someone else asked. Pressure the Americans who donate to the settlers, and call your congressmen, Mr. Nawajah said.

"I have to honestly say, the occupation is not just Israeli," he added. "It's American as well."

A quick walk through the divided house of worship above the Cave of the Patriarchs — Muslims on one side, Jews the other, with padlocks and soldiers enforcing the split — set the mood for the group's visit to Hebron. Jewish settlers were attracted to Hebron by the belief that the cave holds the remains of Adam and Eve, Abraham and Sarah, Isaac and Rebecca, and Jacob and Leah.

Outside, Ms. Ofran told of violence including the massacre of 67 Jews in Hebron in 1929, and of 29 Muslims gunned down by a settler as they prayed in 1994, which ushered in a period of Arab suicide bombings.

She was leading the group on a thousand-yard tour along what were once some of Hebron's main market streets, until Palestinians were forbidden to use them, even to get to their front doors. Today they are a graveyard of abandoned storefronts and apartments, as well as some homes where Ms. Ofran said settlers had moved in illegally after the Arab owners, demoralized by restrictions and harassment, had fled.

"People aren't kicked out," she said of the Palestinians who had left. "It's unbearable to live here."

At a last checkpoint, Arabs crossed into the Israeli-controlled section, where soldiers protect 800 settlers from the city of 200,000 Palestinians beyond the gate. Pointing up a steep street to an Arab neighborhood, Ms. Ofran said cooking gas could not be delivered there by truck; people had to carry the tanks on their backs.

The only Palestinian vehicle allowed in, she said, was a garbage truck.

"This is all really sad," said Liyah Foye, 19, a senior at the University of North Carolina-Asheville.

Ms. Foye, who as a black Jew said she had experienced more than her share of bigotry, said she was hit hard by the idea that a "state founded to protect one marginalized group" was oppressing another.

She said she had always loved Israel and seen it as a "beacon of light." But what she saw on Sunday overwhelmed her: "My joy and my light shouldn't be coming from someone else's darkness," she said.

"After today I can no longer stand by," she added, saying she wanted to go home and educate American Jews about the Palestinians' plight. "Even if I'm not oppressing them, I'm still part of the system that is," she said. "My job is to say to my community, 'No, this can't happen.'"

As the day grew long, the facial expressions more pained and the questions more anguished, the J Street tour seemed increasingly incompatible with Birthright's goal of hooking young American Jews on Israel.

By dinnertime, two participants said they were reconsidering their belief in a Jewish state. Jesse Steshenko, 19, of Santa Cruz, Calif., who has a Star of David tattooed on his right wrist, said he was "disgusted" with Israel's government.

"I came in here a very ardent Zionist," he said. "You never know when a Holocaust might happen again. Yet, coming here, I'm starting to doubt whether a two-state solution is possible — and whether Zionism is even worth pursuing anymore."

Yet Mr. Steshenko also said he had made up his mind to make Israel his home after he graduates from college, "to do the work that I think should be done."

Yael Patir, J Street's top official in Israel, pointed to Mr. Steshenko's decision as a sign of success.

"We knew that their days in the West Bank would be the most challenging and difficult," she said of the group. "But we also know that it's the reason they came for the trip."

There remained the question of how much Birthright itself might borrow from a trip like this, if it chose to.

But Channah Powell, 20, a pre-med student at Tufts University, warned against taking the J Street experiment as a model.

"You can't just next year have 50,000 kids on a trip like this," she said. "You have to change the way we're educating them." She added that Jewish groups, schools and synagogues needed to teach their young people about the occupation, not merely wait or pray for it to end.

"American Jewish kids," Ms. Powell said, "have to be able to come on a trip like this without feeling so blindsided."