When carrying out monitoring visits last term, inspectors found that schools "tended to lag behind" on curriculum development in certain subjects, Ofsted has said today.
In other comments specific to primaries, the watchdog said that while schools had "rightly prioritised developing the teaching of reading", some parents "needed more guidance than schools provided" for home learning.
Meanwhile, struggling older children "were not always given the support they needed", according to Chris Jones, Ofsted's director of corporate strategy.
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In a blog published today, Mr Jones reflected on the watchdog's spring term monitoring visits to those schools graded "requires improvement" or "inadequate", which were mainly carried out remotely.
He acknowledged that "schools have had a tough year – to say the least", and "what we found was largely very encouraging".
However, he reported that there was "usually more work to be done" on the curriculum, with thinking and planning in foundation subjects tending to "lag behind maths and English".
"Based on previous inspections, aspects of the curriculum were often an area for improvement in these schools," he wrote.
"So, it was good to see so many leaders giving careful thought to improving their curriculum. While the pandemic has understandably slowed things down, development was still taking place, including training for staff.
"There was usually more work to be done, though. This was often in foundation subjects, where curriculum thinking and planning tended to lag behind maths and English.
"And now, of course, schools are dealing with the challenges of children having had very different experiences to each other during the three national lockdowns. This has some serious implications for planning and delivering the curriculum."
Mr Jones also raised concerns about the teaching of reading at both primary and secondary level.
He said that, in primaries, Ofsted found that "some parents needed more guidance than schools provided to help their children with reading at home".
"Older primary pupils who could not read well were not always given the support they needed to keep improving either," he added.
And there was a "mixed picture" in secondary schools, Mr Jones said.
He wrote: "Some schools had included whole-class reading as part of their 'form time' in remote education sessions, or set expectations that pupils should read daily. Some had provided online books.
"But for pupils who struggled to read, there tended to be little, if any, reading work going on unless they were actually attending school. Reading was an area that inspectors sometimes asked secondary schools to work on further."
Mr Jones said leaders had been "working hard" to understand the gaps in children's learning that have emerged over the past few months.
But he said this will depend, in part, on their quality of assessment while children were learning from home.