Students' lunches are carefully monitored to ensure children receive the healthy brainfood they need, a Whangarei principal says.
Horahora Primary School principal Pat Newman says high-sugar foods like fizzy drink and lollies are discouraged.
"We sit all our kids down and we quietly walk around when they're eating and check their lunch boxes," Mr Newman said.
"We pick up a pattern of the kids who are either always bringing unhealthy [food] or don't have enough and we tend to quietly try and do something about it."
With many schools set to resume next week, a nutritionist is offering parents healthy tips for kids' lunch boxes to help them concentrate in class.
Mr Newman said children and parents were encouraged to pack lunches with nutritional foods.
"But, the reality is I would prefer children to have food than no food, whether it is healthy or unhealthy."
Some families have to make ends meet with very little, he added.
Healthy Food Guide nutritionist Claire Turnbull says children should have a mix of wholegrain carbohydrates, protein and dairy in lunch boxes.
"If your children are eating well at school, they're more likely to concentrate better, feel better, have more energy, be less irritable and get more out of their school day."
She recommended parents involve children as much as possible in the kitchen.
Cheap ingredients like rolled oats, potatoes and eggs could be used as basic components in many foods, she said.
"There are healthy versions of muesli bars you can make at home which have oats and seeds and raisins. You've got a double winner there - you've made something which is like a treat and ... the child has seen what's gone into that food."
Budget-friendly options for lunch boxes included pita-pockets stuffed with tuna, and homemade egg, vegetable and potato frittata. Vegetable gardens were another great money-saver which kids could help grow, she said.
Filling lunch boxes with nutritional ready-to-eat food was also important.
"If an orange is cut up in quarters and they can bite it straight away, they are probably more likely to eat than if they've got it whole and their friend next to them has a bag of chippies," Mrs Turnbull said.
Research from Canterbury University, which surveyed 1000 primary and secondary schools about health issues, found in nearly 60 per cent of schools, teachers identified food in crinkly packets, junk food, foods high in fat and sugar, high-energy drinks and foods high in caffeine and low in nutrients, as barriers to learning.
Hungry children will struggle to concentrate in the classroom.