Since Russia invaded Ukraine in February 2022, the Kremlin has been severing ties with the West that were built up over decades. It has left European treaties on human rights and the prevention of torture, entered into others aimed at countering what it calls Western hegemony, and suspended its participation in nuclear arms treaties.

Education has also been the target of an accelerating crackdown. Late last month, Russia’s prosecutor general declared the International Baccalaureate, a Geneva-based nonprofit whose educational framework is offered at more than 6,000 schools in 160 countries, a criminal organization.

A week before the first day of classes, on Sept. 1, the more than two dozen Russian schools using the I.B. curriculum had to suddenly abandon it. The organization’s activities were prohibited, leaving anyone in Russia who cooperates with it vulnerable to asset seizures or jail time.

“It was such a shock,” said Daria, 42, who teaches at an elite Moscow high school that offered the program. She requested that her last name be withheld to avoid retribution from the authorities. “The country is turning inward,” she added, speaking by phone from Moscow. “It’s beginning to look very much like North Korea.”

The Russian Office of the Prosecutor General defended the ban by saying that the International Baccalaureate’s goal was “to format Russian youth according to Western templates,” accusing the organization of “stoking anti-Russian propaganda and hatred between nations.”

In a statement, the International Baccalaureate said it regretted that Russia’s decision could interrupt students’ education. The organization noted that it had successfully worked in places with shifting political and educational landscapes. Its program began as a way for international schools to provide a globally recognized credential, and it has long emphasized engagement with world cultures.

Russia’s efforts to reshape education, infusing schools with nationalism, militarism and what it calls traditional values, go well beyond the crackdown on the International Baccalaureate.

While the campaign has been underway for nearly a decade, it has rapidly accelerated during the war in Ukraine. President Vladimir V. Putin has been one of its biggest advocates.

The sweeping changes “are taking place at all levels, from kindergartens to universities,” Mr. Putin said last week in a recorded video address on Knowledge Day, the first day of school.

The Russian state, he promised, will do everything to ensure “that our children love their motherland with all their hearts, respect their elders, value friendship and camaraderie.”

In 2024, high school students started taking a class called “The Basics of Defense and Defense of the Homeland,” which includes some simple military training. Next year, a new subject, “Spiritual and Moral Culture of Russia,” will be compulsory for students in grades five to seven. The textbooks are being developed with the Russian Orthodox Church.

The International Baccalaureate program was introduced in Russia in 1996 and expanded to more than 50 schools. Kremlin insiders started private I.B. schools, and officials like Foreign Minister Sergey V. Lavrov spoke at their events and even sat on their boards.

While the program was considered good enough for the children of high-ranking officials and oligarchs, conservative members of the Russian elite started targeting the International Baccalaureate last year.

Anna Y. Kuznetsova, the conservative deputy speaker of Russia’s lower house of Parliament, issued a request to investigate every school with an I.B. program.

The decision to outlaw the organization affected the 29 International Baccalaureate schools that remained in Russia. In a social media post, Ms. Kuznetsova said that the organization was “conducting illegal activities that harm our children.”

Olga Orlova, editor in chief of T-Invariant, an outlet focused on academia, said that the ban was a disheartening signal to Russians who “still hope to maintain some kind of normal relations with the international intellectual and educational community.” She noted that the I.B. curriculum did not even teach about the last two decades of Russian history.

Ms. Orlova, who works in exile, said that the move reflected the Kremlin’s terrified reaction to the outpouring of youth support in recent years for the opposition leader Aleksei A. Navalny. Mr. Navalny died under mysterious circumstances last year while serving prison sentences in an Arctic penal colony.

Daria, the teacher in Moscow, said her school had offered both the International Baccalaureate and Russian curriculums. Some parents had sought new I.B. schools abroad for their children, she said, while others were still weighing whether to adapt to the ideology-infused Russian curriculum.

“It’s a real shame because the smartest kids and the best teachers will be leaving the country now,” she noted.

Yulia Fedorova, a lawyer whose daughter is a recent graduate of an International Baccalaureate program in Moscow, said she thought it was “stupid” to ban the curriculum. But she said she believed that it was still possible to get a good education in the Russian system.

Her daughter, Masha Bryanskaya, 22, said she was sorry to see the program prohibited.

“The intellectual freedom I saw in I.B., I’ve never seen it in a Russian school or Russian exams; there you need to write the correct answers, and not what is true,” she said.

Alina Lobzina contributed reporting.