Children are turning up for school cold, hungry and wearing unwashed or unsuitable clothes because their families are facing money problems, teachers are warning.
In some cases, youngsters are arriving for lessons unable to concentrate and without the right equipment for class, according to a poll.
The findings, published by the NASUWT teaching union, reveal the impact of financial hardship on the nation's children, with some teachers telling stories of pupils "hugging radiators" to keep warm, bringing in mouldy food in their lunch boxes and getting upset when they lose basic items such as pencils and rubbers.
It comes as a separate study found that some children are missing out on school trips because they are too expensive, while others are unable to study music or arts-based subjects due to the cost.
The NASUWT's findings show that almost three-quarters (74%) of teachers have seen pupils coming to school hungry, with 80% saying that youngsters had been lacking in energy and concentration because they were eating poorly.
More than four-fifths (82%) said they had seen pupils turning up for school in inappropriate clothing, with similar proportions (88%) saying children had clothes that were unwashed, or damaged and frayed.
One teacher said they had seen "a child being possessive and anxious about their personal possessions and becoming very upset when they lost a pencil and rubber because 'they were really expensive'".
Another claimed: "One child told a teacher they weren't always able to feed their dog, so sometimes he will give his food to the dog."
The poll reveals that nearly a third (32%) of teachers had seen pupils arrive or leave school mid-year because they had been forced to leave their homes, while 27% said they had experience of students losing their homes due to financial problems.
One NASUWT member said: "I have never known such abject poverty as my pupils are suffering at the moment."
Another said they had seen "children practically hugging radiators, children eating at friends' houses because they don't have food at home, mouldy food in packed lunch boxes".
More than a fifth (22%) of those surveyed had lent or given pupils money, while 27% had provided food, 63% had given or lent equipment and 15% had offered clothing to youngsters, the poll found.
NASUWT general secretary Chris Keates said: "Teachers and other public service workers are struggling to pick up the pieces caused by this Coalition's economic and social policies.
"Poverty and homelessness take a physical and emotional toll on children.
"They often suffer more ill-health and absenteeism from school, cannot concentrate when they are in school because they are tired and hungry, have no space to do homework and have to travel long distances to get to school from temporary accommodation."
The NUT's study, based on a survey of around 400 young people, revealed that of those from low-income families, more than one in four (27%) had chosen not to study music or art at school due to the associated costs.
And more than half of poorer pupils (57%), along with 28% of better-off students, revealed that they had missed at least one school trip because of the price.
The study also found that some poorer students did not have a full school uniform because of the cost, while others said they did not have all the books and equipment they needed for lessons.
NUT general secretary Christine Blower said: "We take the common-sense view that schooling is free in this country, in the sense that there are no school fees if you go to a state school, but actually there are quite significant financial barriers for the children who come from poorer homes."
A Department for Education spokeswoman said the Government was taking "decisive action" to help disadvantaged pupils.
"Around 1.3 million children currently receive a free, nutritious meal at school. We are extending this to all five to seven-year-olds in state-maintained schools from September and allocating more than £1 million to help schools establish more breakfast clubs," she said.
"We have invested in the Pupil Premium, raising it from £625 million in 2011-12 to £2.5 billion in 2014-15. This is giving schools the additional resources they need to raise disadvantaged pupils' attainment, and give them a better start in life."
*The NASUWT questioned almost 4,000 teachers between February 28 and March 17 and the NUT's research is based on a survey of 399 young people.