Pupils were left in tears after a teacher told them that an asteroid was about to hit Earth and kill them all.
Pupils were told an asteroid was on a collision course with Earth
The spoof announcement was designed to teach 14-year-olds the importance of
seizing the day but backfired after they became visibly frightened.
Keith Hogan, head teacher at St Matthew's RC High School in Moston, Manchester, said he regretted any distress caused to the 230 pupils.
The head of year behind the assembly "stunt" later moved to reassure them.
He had told the year nine students that the asteroid was on a "collision course".
It is also believed that the students were told that they should go home and say "final farewells" to their families.
The teacher then admitted the story was a stunt aimed at underlining the theme of the assembly - "living each day to the full".
Head Mr Hogan said: "Obviously I regret the fact that any student was distressed by the content and delivery of the assembly.
"However, I am confident that the head of year acted appropriately and professionally in dealing with the incident.
"Following the assembly the head of year visited every year nine class and again told the students that the story was untrue and made every effort to ensure that
those students who had been anxious were reassured."