More than one in four primary school pupils in England were taught on-site last week, Government data shows.
Nearly a fifth (18%) of state school pupils were in class on February 25, up from 16% on the week before half-term, according to figures from the Department for Education (DfE).
The rise came after the Government announced all pupils in England would return to class from March 8.
The data shows that 27% of primary school pupils were on-site on Thursday last week, compared with 24% on February 11.
Pupils in schools and colleges in England, except children of key workers and vulnerable pupils, have been learning remotely since the start of the lockdown.
On Monday last week, Prime Minister Boris Johnson announced that all pupils in all year groups would be able to start returning to face-to-face lessons from next week.
After the announcement, approximately one million children of key workers attended school last week, up from 894,000 on the week before half-term.
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “The number of children on site has been much higher in many schools than in the first lockdown, and it has been extremely unhelpful that the Government has at no point clarified whether there is a safe limit.
“Schools are now focused on the task of reopening to all pupils from March 8. They are very much looking forward to welcoming back all children.
“However, this has been made more challenging for secondary schools by the lack of clear direction from the Government over the use of face coverings in classrooms, as well as the huge logistical exercise of running Covid testing stations.
Figures show that 654,773 devices have been sent to councils, academy trusts, schools and colleges since the lockdown began on January 4 – which is an extra 161,449 devices compared with a fortnight ago.
It comes after the Government pledged to provide 1.3 million devices to disadvantaged children.
Education Secretary Gavin Williamson said: “Everyone working in schools and colleges has been going to extraordinary lengths over the past weeks and months to continue educating our young people, providing care for vulnerable children and juggling the demands of having some children in school while most receive their education remotely.
“We are hugely grateful for all the work under way to prepare for students’ return to the classroom next week.
“The extra safety measures in place, including asking secondary students to wear face coverings in classrooms, as well as the comprehensive twice-weekly rapid testing on offer to students and families should provide extra reassurance that we are taking every opportunity to reduce transmission of the virus and keep everyone safe.”