Reopening primary schools to some year groups next week could have a "detrimental impact" on the quality of learning for pupils at home, heads have warned.
Paul Whiteman, general secretary of school leaders' union NAHT, said fewer teachers will be available to support children with remote learning if pupils in Reception, Year 1 and Year 6 are taught in smaller groups from next week.
His comments came ahead of the government's final decision on whether to reopen primary schools in England to more pupils from as early as Monday.
On Wednesday, school standards minister Nick Gibb said it was "difficult to say" whether the government's aim to get all primary school pupils back in class before the summer break will occur.
Addressing MPs on the education select committee, he said: "Remote education, home education, will continue for the majority of pupils and young people – probably until the end of the summer term."
Findings from NAHT suggest nearly three in five (57 per cent) schools are providing home learning resources for pupils daily and more than a quarter (29 per cent) provide them weekly.
The survey of 4,784 school leaders, carried out earlier this month, also found that the majority of schools have been creating their own online resources as well as liaising with parents about home learning.
But NAHT is concerned that the quality of remote learning on offer for the year groups that will not be returning to school in the summer term may suffer amid a wider reopening of schools in England.
The government's guidance says primary school classes should normally be split in half, with no more than 15 pupils per group and one teacher, and children should be kept in the same groups all day.
Mr Whiteman said: "Splitting classes in order to reduce the risk of transmission requires twice the number of staff, leaving fewer teachers to support those other children still at home.
"I worry that an unintended consequence will be a detrimental impact on home learning. I know the profession will continue to do all that it can, there are no easy answers."
Last week, Christopher King, chief executive of the Independent Association of Prep Schools (IAPS), said some private schools may decide to remain closed to Year 6 pupils who can continue virtual learning.
Mr King said: "The schools need to be confident that what they're going to offer will be superior to what they can do online.
"If you're asking teachers on top of that to perform two tricks at the same time, to deliver online and teach in the classroom, we may be asking just too much."
On Wednesday, MPs questioned Mr Gibb about what the government is doing to monitor the quality of online learning being offered by schools to children at home amid concerns that pupils are missing out.
He acknowledged that motivating children at home was "a challenge" for parents, but added: "The teachers we come across are doing a superb job in making sure children continue their education while at home, but ultimately we need to get children back into school because education will never be as good as it is when children are in a classroom with their teacher, and that's the ultimate objective to get back to that system."