More children are going to school hungry due to a lack of money and interest from parents in providing a decent breakfast, research has suggested.
Four in five teachers claim their pupils are turning up for lessons hungry, with 55% saying the numbers have increased in the past year, according to the report by Kellogg's.
Two thirds of the 500 teachers surveyed said the main reason that children are arriving unfed is because of apathy by parents, while a similar proportion (69%) cited a lack of time at home.
The survey concludes that families suffering financial hardship is also an issue, with 57% of teachers suggesting a lack of money is to blame for pupils going to school hungry.
In a bid to solve the problem, the report found that many teachers are buying food for youngsters out of their own pocket.
Nearly one in three (31%) of the teachers questioned said they take food into school to give to hungry pupils, with 16% of primary teachers saying they spend up to £24.99 a month feeding youngsters.
But this food is not always healthy - while 60% take in fruit and 45% bring in cereal bars, rice cakes and healthy savoury snacks, 17% take in sweets, cake and chocolate, the report claims.
It warns arriving for school hungry can impair a child's concentration, cause behavioural problems and impact on learning.
Asked how hunger can affect pupils, some 93% of teachers said it decreases concentration, 87% said it increases tiredness, 73% said it affects attainment and 71% said it leads to poor behaviour.
The report, published to mark the launch of Kellogg's "help give a child a breakfast" campaign, suggests that breakfast clubs are a cost-effective way to ensure that children eat before lessons, but adds research has found that many clubs in schools across England have closed in the past year due to lack of money.
Karin Woodley, chief executive of education charity ContinYou, said: "Many families are really struggling financially and, in extreme cases, this means that there simply isn't enough food to go round. Breakfast clubs can provide a lifeline for these families so we're extremely concerned to hear that many are being forced to close."
Earlier this year, a survey by the Association of Teachers and Lecturers (ATL) found that England's young children are being served "very small" school dinners and given limited choice despite paying more for their meals.
It revealed that almost a third of teachers do not believe that school meals are value for money, with some warning that pupils are often being given chips, pasta and rice rather than vegetables and salad.
It also found that there has been an increase in free school meals - a measure of poverty - as more families are hit by economic problems.
A Department for Education spokeswoman said it was "worrying" to hear of any child going hungry, insisting that the Government had protected the schools budget and introduced the pupil premium, which is dedicated funding for the most disadvantaged pupils.
The Opinion Matters survey for Kellogg's questioned 500 teachers between August 7-21.