The majority of pupils have slipped back in their learning during the coronavirus pandemic, Ofsted chief inspector Amanda Spielman warns today.
Ofsted has found that some pupils have lost stamina in their reading and writing, others have lost physical fitness and some are showing signs of mental distress.
The inspectorate has published its second major report detailing the findings of its visits to schools this term to check on how pupils are being supported on their return to full-time education.
Closing the gap: Lockdown's challenge for teachers
In a commentary about the report, Ms Spielman said: "It’s becoming clear that children’s and learners’ experiences since the first national lockdown in March fall into three broad groups.
Coronavirus: Ofsted warns of pupils falling behind
"There are those who have been, and still are, coping well in the face of restrictions; there is a group who have been hardest hit, largely because of the interplay between their circumstances and the impact of the pandemic; and there is the majority – a group who have slipped back in their learning to varying degrees since schools were closed to most children and movement restricted."
Ofsted said its inspectors found that children’s experiences weren’t necessarily determined by privilege or deprivation.
It added: "Rather, those who are coping well have good support structures around them and have benefited from quality time spent with families and carers.
"This includes children from all backgrounds, including those within the care system, some of whom who saw relationships with carers improve."
Ofsted is checking on more than 1,000 schools this term through visits, which do not result in an inspection grade.
However, the watchdog is publishing a letter with its findings about each school.
A Tes analysis of the first set of the letters from these visits, published last month, showed that pupils slipping back on phonics and maths was a recurring theme.
The new Ofsted briefing report, published today, says nearly all primary school leaders who were visited said they were "prioritising reading and mathematics, with very few schools focusing on science".
The report adds: "Some also talked about needing to work on pupils’ writing, including their ‘stamina’ when writing at length. They felt that pupils had lost this ability during the first national lockdown, when they had not had the chance to practise their writing style and posture. Almost all the schools were concentrating strongly on phonics."
Ofsted's report says that primary school leaders most commonly identified that pupils had lost some of their knowledge and skills in reading.
Some leaders said that writing was also an issue, including writing at length, spelling, grammar, presentation, punctuation and handwriting.
The report adds that literacy and maths were a concern at secondary school level, along with more practical subjects, such as PE, design and technology and music.
Secondary heads also told the watchdog that students had fallen behind, in particular, in modern foreign languages.