His comments come after the UK’s chief medical officers issued a joint statement seeking to reassure parents that it was safe for children to return.
Boris Johnson has issued a plea to parents to send their children back to the classroom when schools reopen next month.
The Prime Minister said the risk of contracting coronavirus in schools is “very small”, and that pupils face greater harm by continuing to stay away from the classroom.
Many pupils in England have not been to class since March when schools were closed except to look after vulnerable children and those of keyworkers.
Schools in Scotland reopened earlier this month, while those in England, Wales and Northern Ireland are expected to welcome all pupils from the beginning of September.
Mr Johnson said: “I have previously spoken about the moral duty to reopen schools to all pupils safely, and I would like to thank the school staff who have spent the summer months making classrooms Covid-secure in preparation for a full return in September.
“We have always been guided by our scientific and medical experts, and we now know far more about coronavirus than we did earlier this year.
“As the Chief Medical Officer has said, the risk of contracting Covid-19 in school is very small and it is far more damaging for a child’s development and their health and wellbeing to be away from school any longer.
“This is why it’s vitally important that we get our children back into the classroom to learn and to be with their friends. Nothing will have a greater effect on the life chances of our children than returning to school.”
His comments come after the UK’s chief medical officers issued a joint statement seeking to reassure parents that it was safe to send their children back to school.
They said “very few, if any” children and teenagers would come to long-term harm from the virus solely by attending school, while there was a “certainty” of harm from not returning.
Liberal Democrat education spokeswoman Layla Moran said: “The Government must rapidly upscale Test and Trace and ensure schools have the mental health support, financial resources and the use of community spaces they need ahead of opening fully.
“The country, and seemingly the Prime Minister, has lost faith in Gavin Williamson. To restore confidence among parents, pupils and teachers the best thing the Prime Minister could do is sack him, rather than speak for him.”