One-in-five children at a low-decile school don't have enough food in their lunchboxes, according to new data collected by a child poverty charity.
KidsCan says it can get worse at this time of year, after uniform and stationery shopping.
Chief executive Julie Chapman says food isn't all children are missing out on.
- NZ's child poverty highlighted in Amnesty report
- Child poverty falls for first time in years - but more work still needed
Ms Chapman says it can seriously impact a child's learning, with 93 percent of children from 'advantaged' communities passing NCEA level 2, but only 68 percent of those in 'disadvantaged' areas.
"Not having adequate nutrition impacts in all sorts of areas of a child's life - certainly brain development, learning ability, ability to concentrate at school."
And it gets worse as payday approaches.
"One of the things that we see a lot of is children who are coming to school with some food, then by the end of the week they've got nothing or very little."
Ms Chapman says some schools have stopped charging fees, just so families can afford to send their kids.
KidsCan says in the schools it operates, it's now helping to feed 20 percent of pupils.
In 2018, the charity says it gate out 5.27 million items of food, including 245,000 servings of baked beans and more than 130,000 loaves of bread - up 20 percent on the year before.
In addition to food, KidsCan gave out nearly 50,000 jackets, 28,000 pairs of shoes and socks and 22,000 boxes of tampons, pads and liners.
The charity now operates in almost twice the number of schools as it did just five years ago.
Last month, the Government passed Prime Minister Jacinda Ardern's signature Child Poverty Reduction Bill, which requires the Government to set and monitor child poverty reduction targets.