Murder is not among the usual playground games chosen by children. But Philip Dutton, one of the clinical psychologists who worked with the young survivors of the Dunblane massacre, says traumatised children tend to play games re-enacting the events that haunt them.
"Often young children will play at killing afterwards," he said. "But they don't tell the adults because they don't want to upset them, just as the adults don't want to mention it and upset the children. There's a fear that they only got some of us this time, so they'll come back and get the rest.
But, with work, they can get their sense of safety back."
On March 13 1996, Thomas Hamilton, a lone gunman, walked into the gym at Dunblane primary, in the Scottish borough of Stirling, and gunned down a class of five and six-year-olds. He then walked into the next-door classroom and shot at a group of 11-year-olds in a maths lesson.
Catherine Gordon, their teacher, yelled at the pupils to "hit the ground", an order which saved their lives. In total, Hamilton fired 105 rounds of ammunition, before turning the gun on himself. Sixteen of the 28 children in the gym died, along with Gwen Mayor, their 47-year-old teacher.
It was the worst killing of its kind in Britain. Terrified parents across the country demanded security locks and entry phones on all schools, which began to hire bouncers or fit panic alarms.
Dunblane parents and teachers subsequently launched the Snowdrop campaign, lobbying for tougher gun laws. They eventually secured a total ban on handguns, and tighter school security.
Ten years on teachers, local authority workers and parents in Dunblane are unwilling to talk about the shooting. But Mr Dutton was among the psychologists called in to help children cope with the aftermath.
"You don't have to have post-traumatic stress for something like this to wreck your life," he said. "Some of the children who have left school now still have daily or weekly thoughts about these occurrences. Some don't have jobs, don't go out, or are agoraphobic. Or they could live in a normal way, but small things make them jump."
A car going past quickly, for example, could trigger disproportionate fear.
Children might experience flashbacks, or sleep uneasily. Such long-term anxiety could lead to full-scale depression.
"Bereavement and trauma are rolled into one," said Mr Dutton. "And there will be a level of guilt as well. It's not logical, but it is emotional.
"You carry that guilt with you, so you can't move on. It's hard to lose that without help."
Psychologists advocate therapy for all involved in school-based trauma.
Pupils also require a sense of safety and continuity, according to Michael Hughesman, who provides post-traumatic psychological support to schools.
A speedy return to normality is vital, but maintaining the illusion of normalcy can be taxing for teachers.
"Pretending things are normal is emotionally exhausting," said Mr Yilmaz.
"It's a big strain. But teachers are generally pretty emotionally literate.
They work together as a group and support each other.
"Teachers are holding themselves together for the pupils, but heads are holding themselves together for the children and the staff. They are the ones dealing with the publicity, the media and the local authority. It can be isolated at the top. We need to be sensitive to that."