Four out of five schools with the poorest pupils in England and Wales do not have enough devices and internet access to ensure all self-isolating pupils can keep learning, according to a leading education charity.
The lack of equipment means schools were having to dip into alternative budgets and that it was the the poorest pupils' education that suffered during self-isolation, Teach First warned.
A socio-economic divide was also underlined by the finding that schools with the most affluent intakes were nearly three times (29%) more likely to use donations to pay for digital devices compared with schools with the poorest pupils (10%).
The scale of the need for devices to facilitate online learning during the pandemic was "enormous", said one headteacher, commenting on the survey carried out for Teach First.
"At our school we soon learned pupils were using smartphones to complete homework rather than accessing the school's online work platform on a suitable device," added Kathryn Hobbs, the headteacher of David Nieper Academy in Derbyshire.
"When it comes to schoolwork, a smartphone just isn't sufficient - but the hard truth is that some families simply can't afford the most appropriate IT equipment. For schools to continue to support all of their pupils throughout this pandemic, we need more access to IT devices, but looking into our budget, there's not enough money to meet the need."
The survey - which also found that nearly three in four (73%) school leaders said they do not have enough digital devices and internet access to ensure all self-isolating pupils can keep learning - was based on data collected by Teacher Tapp, a daily survey app that questioned more than 8,000 teachers each day.
Teach First's chief executive, Russell Hobby, said: "It's not right that some children will fall further behind at school simply because their families can't afford laptops and internet access."
A spokeswoman for the Department for Education said it had purchased more than 340,000 laptops this term to support disadvantaged children. "By Christmas, this will be an injection of over half a million since the pandemic hit," she added.
This was part of more than £195m invested to support remote education and access to online social care, she said.
"We are entirely committed to ensuring as many disadvantaged children as possible benefit from receiving a device this term, and ensuring no pupil, no matter their background, loses out on an outstanding education."
Separately, the DfE has asked schools that are not using 4G wireless routers that have been distributed to sign up for a scheme in which they can be handed back and "reallocated" to other pupils.
Schools are being urged to sign up to an online portal to see how much data is being used by each router they're responsible for.
The details were included on Friday in an update to government guidance, which notes that remote learning equipment given to schools during the summer term was owned by local authorities and academy trusts.
It added that those bodies could choose to transfer ownership of the laptops, tablets and 4G wireless routers to individual schools or give devices to care leavers, or children and families with social workers.