Needy pupils are exhausted and struggling to concentrate in class due to hardship at home, teaching staff have warned.
A survey of 1,788 National Education Union (NEU) members laid bare the shocking impact of poverty on children's learning, with 87% reporting their pupils are tired or unable to concentrate (81%).
Two thirds (66%) had seen pupils attend school in dirty, damaged or badly fitting clothes and shoes, while 58% said children didn't have proper school uniform or PE kit to wear.
Nearly 6 out of 10 teachers (57%) noticed pupils were hungry during the school day, and 55% of respondents said that disadvantaged children in their school were frequently ill.
Official figures show 3.9 million children were living in poverty last year - equivalent to 27% of all British kids.
Campaigners have warned that the Government's decision to slash Universal Credit by £20-a-week will push 400,000 children back into deprivation.
Schools were forced to step in during the pandemic to help youngsters struggling to afford basic necessities as Covid wreaked havoc on family finances.
Brits are now being clobbered by the cost of living crisis, with national insurance hikes, rocketing energy bills and price rises all hitting households.
NEU joint general secretary Dr Mary Bousted said: "It is long overdue that the government fixes the visible inequalities in schools which are completely within their gift to correct.
"But schools cannot counter the deep inequality in home learning environments and family income alone.
"The government must urgently commit to a cross-department child poverty strategy."
Some teachers told the survey that they were providing free breakfasts or setting up a food bank at their school.
One head regularly bought winter coats, shoes and other warm clothes for pupils.
Members issued calls to help families by making school uniforms more affordable, offering free internet access to children in households on Universal Credit, and food vouchers for children on Free School Meals during the holidays.
Shadow Schools Minister Stephen Morgan said: "After 12 years of Conservative government more than a quarter of children are living in poverty, and families now face a cost-of-living crisis that threatens to further limit their opportunities.
"Conservative choices are holding children back, preventing thousands from excelling at school."
A Department for Education spokesperson said: "We continue to prioritise support for disadvantaged children across early years, in schools and in further education, including by providing 1.9 million laptops and tablets through the pandemic and introducing new legally-binding guidance requiring schools to make uniform affordable for all.
"Our ambitious recovery plan is also rolling out across the country, with nearly £5 billion invested in high quality tutoring, world class training, extra funding for schools, and extending time in colleges.
"We have expanded access to free school meals more than any other government in recent decades, and are ensuring wider support is available for vulnerable families in need, including through the Household Support Fund."
The survey was conducted online through membership and received 1,788 responses from English state school teachers between 24 February – 8 March 2022.
