The Cancer Society school accreditation initiative, SunSmart Schools, has 56 Bay schools signed up so far, with another 16 seeking accreditation.
Ms Desmarais said some new schools being built in growth areas in Papamoa and Tauranga were struggling with shade creation.
"They've got to design shade into the development of the school, but they have to fundraise because the Ministry of Education doesn't provide them any further money to cover the cost of shade development," she said.
"It unfortunately falls on parents and boards of trustees."
Tahatai Coast School principal Jenny Griggs said every school needed to have a SunSmart policy.
"We have compulsory sunhats during Terms 1 and 4. It's part of the uniform and can be purchased through the school. We have shade cloths up and they'll go up when we have the new buildings up. If the kids don't have hats, they have to stay in the shade.
"We have designated shaded areas, too, where kids can get out of the sun. The other thing we do is we have large bottles of sunscreen on sports days that children can tap in to."
Cost was not a barrier because the school had designated areas where verandas gave shade. The school also had shade cloths.
Papamoa Primary School deputy principal Wayne Whitaker said the school had three shade sails over three eating areas but cost was a barrier to extending that coverage. The school enforced the use of hats in Terms 1 and 4 and had sunscreen available to pupils.
"One of the barriers would be the cost [of the shade sails]. The second thing would be the attitude some children have which comes from home and they question whether hats are necessary or not. We promote it and generally we have the support of most but in the weekend or after school when the kids go home, they have a choice whether to wear a hat or not.
"Some might say the hats we choose are not cool enough and that's a developed attitude that's come from out of the school community," Mr Whitaker said.
Mount Maunganui Primary School and Tauranga Adventist School had SunSmart policies but agreed cost was an issue.
Sun protection has become a major health and safety issue, as sun exposure at an early age affects a child's lifetime potential to develop melanoma skin cancer.
New Zealand has one of the highest melanoma rates in the world and Niwa is forecasting a return to normal summer conditions this year after last season's washout.
The study of 189 schools looked at 12 sun-protection criteria drawn from the Cancer Society's SunSmart Schools Accreditation Programme - including shade provision, sunscreen, hats and clothing, and curriculum content.
Altogether, 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.
Cancer Society Sunsmart Schools programme co-ordinator Louise Sandford said there were barriers to schools implementing sunsmart initiatives.
"There's a difference between becoming signed up and being SunSmart."
The Cancer Society subsidised sunscreen for schools but for some poorer schools even the subsidised cost could be a burden, she said.
New Zealand Principals Federation president Paul Drummond said most schools had SunSmart policies.
"It comes as a bit of a surprise that there would be large numbers of schools ignoring what is common sense ... I don't think schools need convincing."
But Mr Drummond said the cost of providing shade at schools was prohibitive as it was not covered by schools' five-year capital funding programme.
Staying SunSmart
Slip, slop, slap and wrap.
During the hours of 11am and 4pm in the daylight-saving months, keep children out of the direct sun as much as possible - indoors and in the shade.
Even in the shade, other SunSmart actions should be used, as UVR is reflected by surfaces such as concrete, water and sand.
Dress your child in a broad-brimmed hat and close-woven clothing that covers the arms, shoulders and legs.
Use a sun cover over children's pushchairs.
Plan in advance - if there is no available shade, create a shaded play area.
Use a SPF30+ broad spectrum sunscreen and reapply every two hours.
- Source: SunSmart NZ