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 teaching union NASUWT, 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.
The survey, which questioned almost 4000 NASUWT members, found many teachers are resorting to giving pupils money out of their own pocket, providing food and lending clothes to help them out.
The NASUWT said it had commissioned the survey in response to concerns raised by teachers about the long-term impact of Government economic policies on children and young people.
The findings show almost three quarters of teachers have seen pupils come to school hungry, with 80% saying 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 to school in inappropriate clothing, with similar proportions (88%) saying children had clothes that were unwashed or damaged.
One teacher said one child said they weren't always able to feed their dog, so sometimes he would give his food to the dog.
Another said a child became very upset when they lost a pencil and rubber because "they were really expensive".