Headteachers have warned children are turning up to school malnourished, grey-looking and in dirty uniforms as well as stuffing food in their pockets because they are living in poverty.
Some pupils have also failed to arrive to school because they don't have any shoes, whilst it has also been suggested some wear their uniforms at weekends as they don't have any other clothes.
Several primary school teachers spoke to reporters at the National Education Union (NEU) conference in the NUT section in Brighton.
One said that education issues such as league table positions are fast becoming secondary to dealing with the impact of financial hardship among pupils.
A headteacher 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.
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."
She added that her school is running a food bank and also hands out clothing such as winter coats and shoes.
A poll of around 900 NEU members found that 87% think that poverty is having a significant impact on the learning of their pupils.
The Government said it is taking measures to close the attainment gap and to support disadvantaged children.
A Department for Education spokesman said it has 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 £2.5 billion 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."