Parisian nursery teacher Dominique Sicard pored over a 57-page protocol from the French education ministry on how to respect social distancing with a class of five-year-olds and is categorical.
"If the people who govern us think we can respect all this to the letter, there's no point in reopening at all," said the 53-year-old. "I've already warned parents that while children will have a table and chair with their name on, it is impossible for them to remain at that desk all day."
It is a dilemma being felt around the world as countries which imposed lockdowns to stem the spread of coronavirus begin to reopen their schools.
In the UK, the government has asked primary schools to reopen on June 1 for reception, Year 1 and Year 6.
Ms Sicard's Ecole des Trois Bornes is one of tens of thousands of French nursery and primary schools opening its doors to about 1.5 million pupils this week, roughly a quarter of the total. Secondary school children are not due back until May 25.
Among a long list of sanitary measures, teachers must wear masks and children's chairs must be separated to avoid spreading the disease.
One measure Ms Sicard and colleagues have already written off is to coop children inside a metre-square enclosure in the playground far from their classmates.
"It's inhuman and impossible. Five-year-olds need to be able to run around and let off steam, otherwise they lose the plot," she said. "If they see their friends, they'll want to go and play with them."
The return to school is on a voluntary basis and the majority of children remain at home. Teachers are supposed to juggle real and remote teaching.
Unions have criticised the decision to reopen the schools, calling it "premature" and pointing out the government overruled its scientific committee's advice to keep them shut until September.
"Why have we started with the youngest children to end the lockdown when we know they'll be the hardest ones to make apply protective measures?" asked Francette Popineau, chief of the primary school union.
Parents are mixed. Bruno Timsit (41) is keeping his three children away from nursery, primary and secondary school for now. "It wasn't an easy decision but there is no rush. We weren't sure how schools were going to cope and were a bit worried about the kids contaminating each other and us," he said.
However, Tarek Elachkar (45) said he "decided to trust the official guidelines". His nine-year-old daughter, Olivia, will return to primary school today.
"She misses school. We tried to tell her it would be different but she said she was happy to go back. That nailed it for us," he said.
As primary children in the Netherlands began a staggered return, Dutch parents have been instructed to "kiss and go" at the school gates.
Audrey Verschuren, principal of the Leonardo da Vinci School in Amsterdam, which admits half its children in the morning and half in the afternoon, said: "It's a bit nerve-racking for them to see their four-year-old child, who has been with us for just two months, walk into the classroom on their own."
Each school has come up with its own solution to keep the required 1.5 metres between staff and pupils. Ribbons mark out one-way routes, and there are separate entrances for different age groups. Older or vulnerable teachers do not have to return to work, while some schools have taped off a safe area for teachers at the front of class.
At the British School of Amsterdam, a third of parents have kept their children at home, but Paul Morgan, the principal, said: "It has been so heart-warming to see the children back in school, smiling and enjoying seeing their teachers and friends again."
Denmark pioneered the start of the European return to school from May 4 by keeping its primary school children in small groups. That appears to have been a success, so much so the insistence on children washing their hands frequently has led to problems with skin irritation and eczema.
Schools began to reopen in Germany last month, but parents and teachers have voiced frustration with measures to contain the virus.
Most schools have reduced class sizes so social distancing can be observed, but many can only achieve this by dividing classes and teaching children on alternate days.
"It's an absolute farce," one parent in Berlin said, complaining that her child will only get four days of lessons before the summer holidays under the new timetable. Pupils are expected to wear masks while entering and leaving but most schools allow them to be removed in the classroom.
Henry Tesch, headmaster of the Carolinum School in Neustsrelitz, said dividing classes and teaching on alternate days isn't an option because of the long distances his pupils have to travel, so the school is offering coronavirus tests to pupils twice a week.
Switzerland has taken a radical approach because its government is convinced children are not at risk from the virus. "Young children very rarely get infected and transmit the virus to others even less," said interior minister Alain Berset.
Primary and secondary schools were allowed to reopen this week and in most regions they are teaching full classes as usual. A notable exception is Zurich, where classes have been divided in two to prevent overcrowding.
In Taiwan, which has avoided a lockdown due to its successful strategy, schools were closed for February, but have since functioned in a relatively normal way except for some social distancing restrictions.
China, where the coronavirus pandemic began, has been reopening its schools in phases, running classes with a maximum of 20 pupils to allow children to sit a safe distance from each other. (© Daily Telegraph, London)