Rising numbers of children are arriving at school hungry with teachers having to bring in food for them, according to a poll.
The survey, conducted by Kellogg's, found more than a third of teachers in Greater London saw children arriving at school hungry every day.
Nearly a third also suggested children were falling asleep in class because they were hungry or thirsty.
The survey, which questioned almost 900 teachers, found that a fifth believe that the number of youngsters turning up for lessons hungry has increased in the last year, while a further 77% said it had stayed about the same. Just two per cent said they thought there had been a decrease.
Of those that said there had been an increase in hungry pupils, 69% said they thought one of the main reasons for this is due to families continuing to struggle due to the economic downturn, while 56% said benefits cuts are affecting families' financial situations, making it tougher for them to provide breakfast for their children.
Just under half thought that some parents were struggling to find work and cannot afford to put food on the table in the morning.
Three quarters of all the teachers questioned said that being hungry or thirsty makes a child more lethargic, while 83% said youngsters are unable to concentrate and 62% said pupils are unable to learn if they have not eaten properly.
Three in 10 admitted that they have brought food into school for pupils they believe have not had breakfast.
Paul Wheeler from Kellogg's, which commissioned the poll, said: "It's a crying shame that so many children are going to school without having eaten a basic breakfast.
"When your stomach's rumbling it's hard to concentrate on anything else, so it's no small wonder we're hearing about children becoming badly behaved and unwilling to learn when they're hungry."
Kellogg's provides school breakfast clubs for children in deprived areas of the UK.
Last year, research revealed that children are turning up for school cold, hungry and wearing unwashed or unsuitable clothes because their families are facing money problems.
In some cases, youngsters are arriving for lessons unable to concentrate and without the right equipment for class, according to the NASUWT union's poll of teachers.
The findings revealed 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.
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