Lots of young people are hoping to join the protest about the Iraq war at midday on Wednesday, but they haven't got permission to leave school.
This comes after hundreds of students took part in a similar rally on March 7. Things got a bit rough and eight people were arrested.
Police and teachers now say they're worried about children's safety, and they're going to try to stop pupils taking part.
The rally's been organised by a group called the Leicester Students' Stop the War Coalition. Their spokesman said: "I think the last demonstration just showed the strength of feeling people have.
"I would urge school students not to be intimidated by the behaviour of the police and to join our demonstration."