BERLIN — It's been a month since German children began to lead Europe in the post-summer ­return to school, streaming back into classrooms and onto playgrounds, with little aside from masks to differentiate the scene from pre-coronavirus times.

So far, epidemiologists are cautiously optimistic.

The school openings have been accompanied by some panicked closures and quarantines. In the first week, there were 31 clusters — amounting to 150 cases — of the novel coronavirus in schools, ­according to Germany’s Robert Koch Institute (RKI). At least 41 schools in Berlin were reported to have been affected in the first two weeks.

But there have been few transmissions within schools themselves, health experts say, and although the number of new daily cases in Germany has been rising, schools haven’t been identified as a driver of infections.

“It’s looking promising,” said Johannes Huebner, president of the German Society for Pediatric Infectious Diseases. “There have not been any major outbreaks yet. Single cases, but they seem to be manageable.”

While Germany’s full-throttle return to class may provide some assurance for those fretting about school returns in the United States and elsewhere, health experts note that it’s still just the early days — and they warn about extrapolating too much. They say the risk associated with reopenings has a lot to do with the levels of the virus circulating in a community.

“The important thing is you have to keep the number in the community low,” said Huebner, who is also head of the infectious-disease department at Munich’s Dr. von Hauner Children’s Hospital. “This is where the United States will have problems.”

Despite a rise in infections that Germany’s RKI said “must be taken seriously,” the 1,484 new cases reported Friday among the country’s population of 83 million compare with at least 37,876 new cases in the latest U.S. report — more than 25 times as many infections in a population just four times as large.

While Germany has seen an increasing number of cases among young people, health officials have linked that finding to summer travel rather than schools.

“I was expecting more schools to be closed,” said Tobias Kurth, director of Berlin Charité Hospital’s Institute of Public Health. “The fear was that it would spread between children. And that’s not happened at all from the data that I’ve seen.”

One cluster where in-school transmission may have been a factor is in Hamburg. At the Heinrich Hertz School, 26 students and three teachers have tested positive for the virus, and health authorities suspect that at least two students may have been infected by a teacher. The transmission routes, however, are still under investigation. In the interim, grades six and eight are in quarantine, and masks have been made mandatory in all classrooms.

Hamburg School Minister Ties Rabe stood by the decision to reopen the city’s schools, saying Heinrich Hertz was an outlier and emphasizing the importance of in-person education. Students, he said, “need the guidance and motivation from teachers, they need their classmates and their friends, and they need the well-equipped workplaces.”

On the whole, Germany’s experience over the past month is consistent with what European schools observed in the spring, to the extent that they were back in session after the first wave of the virus.

Scotland, which sent students back in mid-August, has been similarly relieved so far. First Minister Nicola Sturgeon said initial indications show that parents and teachers should not be “unduly concerned” about going back to school. Scotland hasn’t seen the spike in infections it feared, and among those students who have tested positive for the virus, almost all contracted it outside the school setting. A pair of high schools in Glasgow, where the health board said there was evidence of transmission “amongst a small number of cases,” may be the exception.

Epidemiologists say they are more concerned about the possibility of virus spread in high schools than among younger children.

In Belgium, public health experts are split about whether the reopening of schools last week helps explain a fresh spike in cases or whether the rise has more to do with summer travel.

So far, no European countries have seen anything like what happened in Israel, where health experts say a return to schools in May contributed significantly to a second wave of infections.

Kurth said that with so much unknown about the virus, and different dynamics in different countries, it’s hard to know why the situation in Israel might be different. Factors such as how seriously a population takes the pandemic may play a role, he said.

“But my honest answer is I don’t know,” he said. “You have to evaluate every little cluster.”

Germany’s states, which are responsible for coronavirus prevention measures, have plans to increase school restrictions if case numbers in local communities grow. For now, students in most parts of the country sit in their classrooms — often two to a desk — as normal.

When some grades went back in the spring, there were efforts to stagger schedules and reduce class sizes. But staffing and space restraints have meant a return to normal class sizes for many schools. There remain attempts to keep students in “bubbles” and limit how much different classes interact.

It was only three days after school started that Sophie-Charlotte high school in Berlin got the news it had been bracing for: A parent called to say two daughters had tested positive.

The local health authority was informed, and 191 students and teachers were asked to stay home. But within a week — after everyone was swabbed and negative results followed two days later — they were back in class.

“I was surprised at how quick it all was,” said Julia Rakow, who teaches German to one of the classes that was quarantined.

Rakow throws open the tall wooden windows of her classroom in line with guidelines designed to get air circulating.

As in most of Germany, school rules do not require masks in class — only in hallways. But Rakow’s class masks up for the most part. “It’s awful to teach with a mask,” she said. “But I feel it’s a social responsibility.”

On the playground outside, where children are allowed to mix freely, English and history teacher Markus Reule expressed concerns about what will happen as winter approaches and it becomes less pleasant to keep windows open.

“It’s going to be frosty in there,” he said. “We’ve been telling students they should bring jackets and expect some really cold sessions.”

The prevalence of normal seasonal coughs and sneezes may sow confusion, while Chancellor Angela Merkel has also warned that the wider coronavirus situation may get worse.

Falko Liecke, city councilor for youth and health in Berlin’s Neukölln district, said there is a lack of clarity over the rules when it comes to children with possible symptoms.

“Many parents are unsure, but also many schools are unsure whether there is a clear plan of action,” he said.

“Snotty-nosed children” have been sent home, even though it is their only symptom, when they should be allowed in class, he said. So far in his district, three schools have had children test positive, with 15 teachers and 150 pupils quarantined.

Testing is being used sparingly, Kurth said. About 1 percent of Berlin schoolchildren are being tested to study the dynamics of spread within schools. Beyond that, only direct contacts of infected children are tested, and generally only once.

Death and hospitalization rates have dropped significantly and seem to remain stable no matter how many people test positive, said Kurth. If that remains the case though the flu season, it may be that there’s less cause for concern.

Rick Noack in Berlin and Michael Birnbaum in Riga, Latvia, contributed to this report.