WELLINGTON, Dec 8 - A study from the University of Otago, Wellington, observed nearly 1300 children from eight randomly selected primary and intermediate schools in Wellington in terms 1 and 4.
It found that just 21 per cent wore a protective hat (wide-brimmed, bucket or legionnaire style) while outside.
New Zealand has the highest melanoma rate in the world, with 70,000 skin cancers diagnosed and 500 people dying from it each year.
Researcher Ryan Gage says the study provides further evidence of the need to ensure sun protection in New Zealand schools.
"Our findings suggest that children may be less sun-safe in school grounds than previously believed," he said.
"Although most schools had a 'no hat, no play' policy, few students actually wore hats."
Mr Gage's co-researcher, associate professor Louise Signal, says the sun in New Zealand is often strong enough to cause skin damage between September and April.
The researchers say that comprehensive approaches to improve sun protection should be encouraged, including the provision of school hats, sun-protective uniforms, and the construction of effective shade.