It was Lea Hammermeister’s first day back at school after almost two months at home and she was already preparing for a test.

Not a math or physics test. A coronavirus test — one she would administer herself.

Hammermeister, a 17-year-old high school junior, entered the tent erected in the schoolyard along with some classmates — all standing six feet apart — and picked up a test kit. She inserted the swab deep into her throat, gagging slightly as instructed, then closed and labelled the sample before returning to class.

It took less than three minutes. The results landed in her inbox overnight. A positive test would require staying home for two weeks. Hammermeister tested negative. She now wears a green sticker that allows her to move around the school without a mask — until the next test four days later.

“I was very relieved,” she said happily. In addition to feeling safe around her classmates and teachers, who all tested negative, she feels like less of a risk to her grandmother, who eats with the family every day.

The self-administered test at the high school in Neustrelitz, a small town in northern Germany, is one of the more intriguing efforts in Europe as countries embark on a giant experiment in how to reopen schools, which have been shuttered for weeks and which are now being radically transformed by strict hygiene and distancing rules.

Restarting schools is at the core of any plan to restart economies globally. If schools do not reopen, parents cannot go back to work.

So how Germany and other countries that have led the way on many fronts handle this stage in the pandemic will provide an essential lesson for the rest of the world.

“Schools are the spine of our societies and economies,” said Henry Tesch, headmaster of the school in northern Germany that is piloting the student tests. “Without schools, parents can’t work and children are being robbed of precious learning time and, ultimately, a piece of their future.”

Countries across Asia have already been making the leap, experimenting with a variety of approaches. In China, students face temperature checks before they can enter schools, and cafeteria tables are outfitted with plastic dividers.

In Sydney, schools are opening in staggered stages, holding classes one day a week for a quarter of the students from each grade. Hong Kong and Japan are trying similar phased reopenings.

For now, Europe is a patchwork of approaches and timetables — a vast laboratory for how to safely operate an institution that is central to any meaningful resumption of public life.

In Germany, which last week announced that it would reopen most aspects of its economy and allow all students back in coming weeks, class sizes have been cut in half.

Germany has been a leader in methodically slowing the spread of the virus and keeping the number of deaths relatively low.

But that success is fragile, Chancellor Angela Merkel has warned.

On Saturday, the reproduction factor — the average number of people who get infected by every newly infected person — which the government wants to stay below 1, crept back up to 1.13.

The school in Neustrelitz is still an exception. But by offering everyone from teachers to students free tests twice a week, it is zeroing in on a central question haunting all countries at this stage in the pandemic: Just how infectious are children?

Evidence suggests that children are less likely to become seriously ill from Covid-19 than adults.

But small numbers of children have become very sick and some have died, either from the respiratory failure that causes most adult deaths or from a newly recognised syndrome that causes acute inflammation in the heart.

An even greater blind spot is transmission. Children often do not have symptoms, making it less likely that they are tested and harder to see whether or how they spread the virus. New York Times News Service