Malnourished, grey-looking, children are turning up to school in dirty uniforms and stuffing food in their pockets because they are living in poverty, headteachers have warned.
In some cases, youngsters have failed to arrive for class because they do not have shoes, while others have been spotted in their uniforms at weekends because they have nothing else to wear, it was suggested.
Speaking to reporters at the National Education Union (NEU) conference, NUT section, annual conference in Brighton, primary school leaders described how children are turning up at the school gates showing visible signs of poverty, such as grey skin and poor teeth, hair and nails.
One said that education issues such as league table positions are fast becoming secondary to dealing with the impact of financial hardship among pupils.
The Government said it is taking measures to close the attainment gap and to support disadvantaged children.
In 2015/16, there were four million children in the UK living in poverty, according to the Child Poverty Action Group (CPAG) - equivalent to nine in every classroom of 30 pupils.
A head from a primary school in Cumbria, who would only give her name as "Lynn", said she was aware of pupils putting "food in their pockets to take home because they're not sure if they're going to get another meal that day".
"In some establishments I would imagine that would be called stealing, but in ours it's called survival," she said.
She described seeing children from a nearby affluent secondary school and comparing them to youngsters who had been to her school.
"My children who have gone from me up to the local secondary school have grey skin, poor teeth, poor hair, poor nails, they are smaller, they are thinner," she added.
The students she had visited at the other secondary had "clear skin, good hair, good nails, strong looking children", she said.
Louise Regan, from a Nottinghamshire primary school said she noticed a difference when taking pupils to sporting events with other schools.
"You think 'our kids are really small', you don't notice it because you're with them all the time.
"When you then see them with children of the same age that are in an affluent area, they just look tiny."
Ms Regan said her school has a food bank, and also gives out clothing, such as winter coats and shoes.
"We've had children who haven't come to school because they didn't have shoes, we've gone and bought shoes, taken them to the house and brought the child into school," she said.
And Lynn said: "We've had situations where as members of staff we've put money in and gone to second hand furniture shops and bought beds."
Howard Payne, from a Portsmouth primary school, said he had opened his school during the snow three weeks ago because he was concerned about youngsters missing out on a hot meal that day.
Around 45% of pupils came in, many of who were eligible for free dinners, he said.
A poll of around 900 NEU members found that 87% think that poverty is having a significant impact on the learning of their pupils.
A DfE spokesman said they have launched a social mobility action plan, which sets out measures to close the attainment gap between disadvantaged students and their classmates and targets areas that need the most support.
He added: "Alongside this we continue to support the country's most disadvantaged children through free school meals, the £2. 5billion funding given to schools through the Pupil Premium to support their education and the recently announced a £26 million investment to kick-start or improve breakfast clubs in at least 1,700 schools."