A Lancashire primary school was forced to abandon a history exercise after it became too realistic for pupils.
Children at St Mary's Roman Catholic School in Bacup were gathered for morning assembly and told that the country had gone to war.
Youngsters were then played Neville Chamberlain's 1939 radio address and taken to the school's cellar.
To simulate the sound of bombs falling staff let a firework off outside.
However, headteacher Mike Richards decided to pull the plug on the day at lunchtime, after some of the children became upset.
"We were doing World War Two as a topic and we saw advice from schools that basically suggested that we introduced the topic as if it was really happening. We didn't foresee these problems," he explained.
"We did a simulated air raid and talked about evacuation, but we said children would probably be evacuated to Bacup as it was safer than Manchester or London."
However, Mr Richards admitted that it may have become too realistic for some.
Meanwhile, children at one Staffordshire primary school made the news last week when they stepped back to the Victorian era.
According to the Sentinel, the youngsters wore Victorian clothing and used slates instead of paper during lessons.