The Canterbury University research shows more than 60 percent of 320 children, aged from five to seven, who have been tracked since they started school in 2013, are showing symptoms of the disorder.
The symptoms include having meltdowns, lashing out at other students, and being tense and irritable.
While the Ministry of Social Development told Morning Report everyone in Christchurch who needed counselling can get it, just 8 percent of the children showing signs of PTSD have had counselling.
The study started in 2013, on the group’s first day at school, and is being headed by associate professor Kathleen Liberty.
“Our data showed that at the end of 2015 – because we followed these children now for three years through Year 3 – that 64 percent of our study children have one or more of these post-traumatic stress symptoms and around 20 percent have six or more symptoms,” she said.
Other symptoms include nightmares, bed wetting, and frequent head and stomach aches.
Professor Liberty said a behavioural study was also done in 2006 and 2007 across similar schools so they were able to compare the results.