Heads have been sent a notice informing them that advice on terrorist attacks is available through the UK Resilience website.
The website recommends that schools prepare telephone numbers for the relevant emergency services. It also warns that children may suffer from long-term emotional trauma. It says: "In some children distress can last for months and may affect academic achievement."
London schools are conscious they are particularly vulnerable to attack.
But teachers elsewhere are sceptical. Ruth Knox, National Union of Teachers secretary in Liverpool, said: "I would consider it scare-mongering."
The Culham Institute, an RE training and research centre, has produced online support material for school assemblies. And teachers' unions have provided guidelines for dealing with any Islamophobia or racist bullying.
For pupils, the fear of impending annihilation is tempered by the knowledge that it provides the ultimate work-avoidance excuse.
Martin Powell-Davies, NUT secretary for Lewisham, south London, said: "I was teaching a group of Year 10 pupils, trying to egg them on to get a bit more work done. But they said there was no point, as they were going to be dead soon, anyway."