Lead author Associate Professor Tony Reeder, director of Otago University's Cancer Society Social and Behavioral Research Unit, has called on the Government to step up.
He said sun protection was a major health and safety issue, as sun exposure in the early years of life had a significant influence on the lifetime potential to develop melanoma skin cancer.
"Yet, as we note in our study, it has become largely the responsibility of a charity, the Cancer Society of New Zealand, to introduce and sustain health promotion efforts in this area."
Dr Reeder said schools that worked with local Cancer Society staff showed positive change.
"We question though whether it should be a non-governmental group's role to shoulder the burden of achieving and sustaining universal uptake of SunSmart practices across all state and state-integrated primary schools," he said.
"We believe public agencies such as the Ministries of Education, Education Review Office and the Ministry of Health need to start taking a similar level of responsibility for sun protection as they do for other health and safety issues in schools."
The study looked at 12 sun protection criteria drawn from the Cancer Society's SunSmart Schools Accreditation Programme - school policy, information provision, hats, other clothing, 'play in the shade', sunscreen, staff role models, curriculum content, event planning, outdoor activities rescheduling, shade provision and policy review.
Schools in Auckland and Northland showed the smallest average improvement across the criteria, while schools in Waikato/Bay of Plenty showed the greatest, followed by Wellington and Otago/Southland.
The greatest areas of improvement were 'play in the shade', rising from 76 per cent to 90 per cent of schools; sunscreen, rising from 66 per cent to 80 per cent; and hats, rising from 61 per cent to 74 per cent.
Some 57 per cent of schools said cost was an obstacle to shade development and 31 per cent to sunscreen use. Thirteen per cent reported limited support from parents.
The study found only 56 of the 189 schools had applied for SunSmart accreditation by the study's end.
Of the 133 schools that had not applied, 61 per cent cited more information and 30 per cent cited better resourcing as encouragement.