The main evidence on the safety and impact of the reopening of schools was published by the government's scientific advisory group, Sage.
Sources involved said the risk of coronavirus for students returning to the classroom was "very, very small, but not zero".
They also said that teachers were not at above-average risk compared to other occupations.
However, there is a lot of uncertainty throughout the board.
There were many requests from within the teaching profession to see the advice, which has led England to seek Reception, Year 1 and Year 6 at the school since the beginning of June. Meanwhile, Scotland and Northern Ireland plan to return to school in August. Wales has yet to make a decision.
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Is it safe to reopen schools?
The documents they say they "cannot be clear" as schools could be reopened without leading to takeoff cases in the UK again.
And while it is clear that children are much less likely to become seriously ill, there is conflicting evidence about the likelihood of being infected or spreading the virus.
A study, published this morning and considered by Sage, showed that children were 56% less likely to be infected than an adult if they were in contact with an infected individual.
In the UK, three children under the age of 15 died from coronavirus
However, a source involved in the development of the council said that any activity outside the home presented risks and that the risk for children to reopen schools was considered low.
They said: "It is totally impossible to say that any change has no risk, as long as the virus is circulating in us, and there is no immunity, there is some risk.
"The risk is low and, in this case, it is not particularly greater than in other environments".
What did Sage advise?
Seven scenarios for opening schools were investigated by Sage and presented to politicians.
He showed that opening daycare centers and reception classes would have less of an effect on the spread of the virus than primary schools. Both had a lesser effect than opening secondary schools.
How different measures can increase the spread of the coronavirus compared to the total opening of schools.
The council says students who arrive in alternative weeks are "good ways to stop long transmission chains at school".
England did not follow precisely any of the seven scenarios. Instead, he is using a combination that would make the reception, years 1 and 6, return to primary school classrooms.
However, Sage said the choice of scenario was significantly less important than maintaining other ways to control the coronavirus – such as social detachment and hand washing.
The reports said: "A more critical issue is adherence to existing measures in other parts of the community".
Sage also emphasized that politicians' next steps must be logical to keep parents on board.
"Failure to do so will influence the number of parents who are willing to send their children to school," the document said.
Current estimates suggest that one in every thousand people in the UK is being infected with coronavirus every week.
Sources said the risk of reopening schools would be less when the number of cases is low, R is below 1 and systems are in place to detect outbreaks and deal with them quickly.
R is the number of people that each infected person transmits to the virus, on average. If it is 2, then 10 infected people will pass it on to 20 others. But if it is 0.5, 10 infected people pass to 5 others.
"The overall [school] risk is not what you would choose as a high risk area for R, unlike dentistry, for example, but it is not zero," said Sir Patrick Vallance, the government's chief scientific advisor.
Asked if all students could return to school in September, he said, "The fewer new infections a week, the greater the chance of getting things done."
A rival group of scientists called "Independent Sage" has also previously argued that schools should not reopen until there is the ability to track the spread of the virus and test anyone who comes into contact with infected people.
He also said that the risk for students would be cut in half if the reopening was delayed by two weeks, as a result of the reduction in cases.
Prime Minister Boris Johnson indicated that 25,000 contact trackers, capable of tracking 10,000 new cases per day, would be in effect until June 1.
Sir David King, who heads the Independent Sage, said: "It is clear from the evidence that we have collected that on June 1, it is simply too early to return. By moving forward with this dangerous decision, the government is risking the health of our communities even more and the likelihood of a second peak ".
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