TOKYO.- In Japan, cultural expectations are repeatedly drilled into children at school and at home, with peer pressure playing as powerful a role as any particular authority or law. On the surface, at least, that can help Japanese society run smoothly.

During the coronavirus pandemic, for example, the government never mandated masks or lockdowns, yet the majority of residents wore face coverings in public and refrained from going out to crowded venues. Japanese tend to stand quietly in lines, obey traffic signals and clean up after themselves during sports and other events because they have been trained from kindergarten to do so.

Carrying the bulky randoseru to school is “not even a rule imposed by anyone but a rule that everyone is upholding together,” said Shoko Fukushima, associate professor of education administration at the Chiba Institute of Technology.

On the first day of school this spring — the Japanese school year starts in April — flocks of eager first graders and their parents arrived for an entrance ceremony at Kitasuna Elementary School in the Koto neighborhood of eastern Tokyo.

Seeking to capture an iconic moment mirrored across generations of Japanese family photo albums, the children, almost all of them carrying randoseru, lined up with their parents to pose for pictures in front of the school gate.

“An overwhelming majority of the children choose randoseru, and our generation used randoseru,” said Sarii Akimoto, whose son, Kotaro, 6, had selected a camel-colored backpack. “So we thought it would be nice.”

Traditionally, the uniformity was even more pronounced, with boys carrying black randoseru and girls carrying red ones. In recent years, growing discussion of diversity and individuality has prompted retailers to offer the backpacks in a rainbow of colors and with some distinctive details like embroidered cartoon characters, animals or flowers, or inside liners made from different fabrics.

Still, a majority of boys today carry black randoseru, although lavender has overtaken red in popularity among girls, according to the Randoseru Association. And aside from the color variations and an increased capacity to accommodate more textbooks and digital tablets, the shape and structure of the bags have remained remarkably consistent over decades.

The near totemic status of the randoseru dates back to the 19th century, during the Meiji era, when Japan transitioned from an isolated feudal kingdom to a modern nation navigating a new relationship with the outside world. The educational system helped unify a network of independent fiefs — with their own customs — into a single nation with a shared culture.

Schools inculcated the idea that “everyone is the same, everyone is family,” said Ittoku Tomano, an associate professor of philosophy and education at Kumamoto University.

In 1885, Gakushuin, a school that educates Japan’s imperial family, designated as its official school bag a hands-free model that resembled a military backpack from the Netherlands known as the ransel. From there, historians say, the randoseru quickly became Japan’s ubiquitous marker of childhood identity.

The military roots of the randoseru are in keeping with Japanese educational methods. Students learn to march in step with one another, drilling on the playground and in the classroom. The school system did not just help build a national identity; before and during World War II, it also prepared students for military mobilization.

After the war, the country mobilized again, this time to rebuild an economy with dutiful, compliant workers. In recognition of the strong solidarity symbolized by the randoseru, some large companies would give the backpacks as gifts to the children of employees.

That practice continues to this day. At a ceremony earlier this year at the Tokyo headquarters of Sony, Hiroki Totoki, the company’s president, addressed a group of 250 rising first graders.

He described the randoseru ceremony — the company’s 66th — as “an important bond that connects families.” After Totoki’s remarks, Sony employees handed out the backpacks, all of them embossed with a corporate logo.

Grandparents often buy the randoseru as a commemorative gift. The leather versions can be quite expensive, with an average price of around 60,000 yen, or $380.

Shopping for the randoseru is a ritual that starts as early as a year before a child enters first grade.

At Tsuchiya Kaban, a nearly 60-year-old randoseru manufacturer in eastern Tokyo, families make appointments for their children to try on different-colored models in a showroom before placing orders to be fulfilled at the attached factory. Each bag is assembled from six main parts and takes about a month to put together.

Shinichiro Ito, who with his wife, Emiko, was shopping this spring with their 5-year-old daughter, Shiori, said they never considered any alternatives to the randoseru.

“It is still the image you have when you think of an elementary school bag,” Shinichiro Ito said. Shiori tried on bags in several colors, including light blue and dusty rose, before settling on a gray leather randoseru that cost more than $500.

Each Tsuchiya Kaban bag comes with a six-year guarantee on the assumption that most students will use their randoseru throughout elementary school. As a memento, some children choose to turn their used bags into wallets or cases for train passes once they graduate.

In recent years, some parents and children’s advocates have complained that the bags are too burdensome for the youngest children. Randoseru can cover half of the body of a typical first grader. Even unloaded, the average bag weighs about 3 pounds.

Most schools do not have personal lockers for students or much desk storage space, so students frequently carry textbooks and school supplies back and forth from home. And in a culture that puts a high value on hard work, patience, perseverance and endurance, the movement to relieve children of the randoseru burden hasn’t gotten very far.

“Those who have no heart say that ‘recent children are weak; back in our day we carried around those heavy bags,’” said Fukushima, the education professor.

A few manufacturers have developed alternatives that retain the randoseru shape while using lighter materials like nylon. But these have been slow to gain traction.

On a recent morning, Kotaro Akimoto, a first grader, left for school carrying a bag that weighed about 6 pounds, about one-seventh of his body weight. Walking the 10-minute route to school, he joined several other classmates and older students, all of whom were carrying a randoseru.

In Kotaro’s classroom, Megumi Omata, his teacher, had posted a diagram of morning tasks, with pictures to represent the order in which the students should proceed. An illustration of a randoseru indicated the stage of stowing school bags in cubbies for the day.

At the end of the day, Kaho Minami, 11, a sixth grader with a deep-red randoseru stitched with embroidered flowers that she had carried throughout elementary school, said she never yearned for any other kind of bag. “Because everyone wears a randoseru,” she said, “I think it is a good thing.”

This article originally appeared in The New York Times.