Up to 80 per cent of Christchurch 5-year-olds are showing post-traumatic stress disorder symptoms, research shows.

As many as four in five Christchurch primary schoolers are exhibiting symptoms of post-traumatic stress disorder (PTSD), a local study has found.

Children who started school in the years after the Canterbury earthquakes were "neurologically different" – and a city-wide focus on resilience has only deepened the crisis, researchers Kathleen Liberty and Maureen Allan found.

The 300 children in the study were five times more likely to exhibit symptoms of PTSD than other Kiwi children. Eighty per cent had at least one symptom and a third exhibited at least six of 12 symptoms. About a third had eight or more behavioural problems.

ALDEN WILLIAMS/STUFF Kathleen Liberty, left, and Maureen Allen have seen "an explosion of interest" in their research into reducing the effects of post-traumatic stress disorder in Christchurch schoolchildren.

Strategies to address the problem suggested by Liberty and Allan have achieved a 27 per cent decrease in behavioural issues since February 2016, sparking "an explosion of interest" in their five-year project, the pair said. Since May, 11 schools and kindergartens had signed up for a duplicate study.

University of Canterbury associate professor Liberty and Resource Teacher Learning and Behaviour (RTLB) manager Allan teamed up for the study after noticing differences in 2012's new entrants.

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JOHN KIRK-ANDERSON/STUFF Linwood North School principal Sandra Smith, centre, says some of the changes suggested by the researchers are challenging for a low-decile school, but have a "profound effect".

"They were clingy, they cried at the drop of a hat, there was less readiness to learn, and there were so many runners," Allan said.

Other problems included toileting issues, lower National Standards results and eating disorders, which the study identified in 45 per cent of its participants.

Liberty said international research indicated the children would have better emotional control after a few years at school, but "we looked at the behaviour in the middle of 2015 and half the children were still a mess or getting worse".

IAIN MCGREGOR/STUFF Mairehau Primary School principal John Bangma says schools are willing to try anything that makes a difference to children's mental health.

Each aftershock disrupted the development of their nervous systems, putting them in a state of "hyperarousal".

The children were "neurologically different": Old, punitive methods of controlling their behaviour only increased their fear, Liberty said.

"One of the things we see in Canterbury is this idea of resilience; there was this myth that children would bounce back from harm.

"Now teachers understand that children aren't doing this on purpose and they're not behaving this way because the teacher is deficient."

Small changes to classroom environments, like removing hanging decorations and amending daily schedules so children play before eating had shown promise in reducing anxiety, the pair found.

Three schools that used such strategies experienced a 27 per cent decrease in the number of children with behavioural problems last year, compared to a 33 per cent rise in behavioural issues at schools that did not.

The benefits were greatest at Linwood North School, which implemented all the strategies suggested by Liberty and Allan, including giving students fish oil and a wholemeal sandwich snack at 10am each day.

Principal Sandra Smith said some changes were "really tricky things to affect within a low-decile setting", but they had a "profound effect on some children".

"I think it would be really difficult to take any one of those strategies away without noticing a difference. They [the children] are calmer, they're happier."

Mairehau Primary School principal John Bangma said his teachers had removed artwork from the windows to let more light in. Its new classrooms would have a neutral colour scheme to limit unhelpful stimulation and the school would look into sleep training next year.

"The kids seem reasonably settled in the playground and they are learning.

"The difficulty is that we don't have a target group that we're saying 'We won't have the strategies for them [for comparison]' … Let's be realistic, we're trying anything that will make a difference for kids."