One in nine pupils arrives at school feeling hungry, according to a new survey of teachers and children.
Figures published today also highlight concerns among teachers that hunger in the classroom is costing children six hours of learning each week.
And two-thirds of teachers warn that children are unable to learn if they are hungry.
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The findings are based on research conducted with 4,000 children and almost 1,000 teachers.
The poll also shows older children are more likely to start the day without anything to eat, with one in six secondary school children not having breakfast.
And girls are more likely to go without breakfast before school, especially in secondary schools, with nearly a fifth not eating in the morning.
For those children at schools in areas of high deprivation, a third said they noticed a child at their school was hungry and gave them some of their food to eat.
Peter Cansell, of the National Association for Primary Education, said: “It’s shocking that in 2019 there are still nearly 800,000 children starting the school day on an empty tummy. This is leading to a shortfall in critical learning time.
“This research even shows that those children that eat breakfast are happier, probably because they have the energy and enthusiasm to enjoy the school day.
"The benefits of pre-school clubs are proven, they ensure that children go into the classroom with the ability to concentrate.”
The research has been carried out by Kellogg's which announced today it is doubling the number of grants it offers school breakfast clubs to support one in four schools in the poorest parts of the UK.
The survey also found that one in seven teachers said that pressure on school funding had negatively impacted their breakfast club provision.
It comes as a council has announced plans to offer a universal free breakfast to every primary school pupil to help local families combat food insecurity.
Hammersmith and Fulham Council is also the first authority in England and Wales to launch a pilot scheme to deliver free lunches in two secondary schools.
The free school lunches will start in January 2020 and be offered to pupils at Fulham College Boys' School and Woodlane High as part of a four-year pilot programme.