We have been reminded again, by the Mayor of London and the Metropolitan Police Commissioner, that a terrorist attack on the capital is inevitable.
London primary schools are having to think about how to protect their children without causing fear and insecurity.
Most seem determined to carry on as normally as possible, otherwise the terrorists will have won. But the issues highlighted by the bombings in Madrid this month go deeper, bringing to the fore the ever-growing complexity of living in a multi-cultural society. British primary schools are overwhelmingly harmonious places, where goodwill prevails and conflict resolution is emphasised. However, it is impossible for the lunacy and strife dominating the outside world not to impinge.
Hermitage primary school, in Tower Hamlets, east London, is overwhelmingly Muslim. The school has decided not to carry on with its regular visits to France, partly because they are worried about hostility towards Muslim children, and because pupils feel uncomfortable about the official French attitude to headscarves, worn by many of the girls at Hermitage.
The pupils have a strong sense of justice and a clear understanding of right and wrong, says head Abdul Hayee. They are against violence, and do not understand why people cannot solve their conflicts by talking.
Nevertheless, some of the Muslim children are divided in their feelings.
"There is no conflict in our school," says Mr Hayee. "The one thing I have picked up is that some of the Muslim children may know what is right and wrong, but still want to take the side of the Muslims."
After the Bali bombing, for instance, in a discussion, some children - although they knew killing was wrong - suggested that Muslims might have felt threatened because they believed other people, such as tourists, were invading their country and felt they had to do something.
In such cases, teachers ask questions to help the children see contradictions in their thinking. They might point out, for instance, that more people come to London every day than go to Bali in three months.
"Being a primary school, it's easy for children to take a view and then change it without feeling guilty. They change it and move on", says Mr Hayee.
Whatever the ethnic make-up of a school, the threat of terrorist attacks affects each one. At Hermitage, staff have become more vigilant, checking the grounds and the cars parked nearby. Chaos ensued when a suspicious package appeared outside the school office window - but it seemed to have fallen off a dispatch motorcycle.
Sir John Cass Foundation primary, the only school in the City of London, is used to being on the alert: it is not far from where the IRA struck in 1993. "The City has been aware of terrorism for the past 15 years said a spokesman for the Corporation. City of London police keep a close eye on the Sir John Cass, and a community police officer drops in at least once a week. Regular fire practice is part of this "warm and close" school's routine.
Jewish schools have to be extra vigilant and all have got tight security, with parents watching out for the safety of the pupils. Laurie Rosenberg, head of Simon Marks primary in north London, said his school has a warm relationship with the nearby North London Muslim Association, with children sending each other cards at Eid and Rosh Hashannah. When it comes to travelling around London, he says, it is important to take extra care, but "what I don't want to do is build a climate of fear amongst the children around public transport".
Martin Francis, head of Park Lane primary in Brent, says if a heightened warning was issued, they would reconsider any planned school trips, but otherwise, "I wouldn't want to put us off using London as an educational resource" - especially as the Mayor had provided free transport for London schoolchildren.
A quarter of his school's population is refugee children and many have experienced war first hand. Park Lane is known for its pastoral work and for its open discussions of controversial issues. When pupils wanted to take part in last year's anti-Iraq war protest, a peace assembly was organised, where children could read poetry and play musical instruments.
Pupils, half of whom are Muslim, get on well together and felt that adults could learn from their example. Mr Francis said it was the apparent irrational behaviour of adults during the Iraq war that frightened them.
During the Kosovan conflict, pupils from the school appeared on Sky television and CNN, talking about war. When the TV crews wanted to come back during the Iraqi conflict, Mr Francis felt that being seen on television could make pupils a target for extremists on either side. Some of the children said they were willing to participate anyway, because they felt strongly about the issues. 'I said: 'I recognise your commitment but I'm not prepared to put you at risk'."
London schools have to hold many emotions at once. One head said after 911 an Asian parent riding on a bus faced abuse, and during the Iraqi conflict parents with Iraqi backgrounds were in tears in the playground. Meanwhile, a Jewish teacher in a nearby school received hate mail.
Recently, said the head, there had been a subtle change in the attitude of some pupils and parents; they had become more fundamentalist, and there was now a slight edge in their relationship with teachers.
Children's behaviour was slightly less respectful, although not rude.
"There are lots of tensions," said the head. But the school has continued to promote its values, stressing that everyone is of value and that fighting is wrong. "That's all we can do, really," said the head.