A campaign to improve the standards of toilets in schools is being taken to the House of Commons.
Half the students said they waited until they got home to use the toilet
Four members of Medway Youth Parliament are to speak at the launch of the Bog Standard Campaign on Wednesday.
They will lobby MPs and present research taken from students at 11 of the 19 secondary schools in Medway.
Half the pupils asked reported problems accessing locked toilets and a quarter said they had suffered health problems by not being able to use the loo.
Lack of privacy
One of the members, Lisa Ellison, said: "As many of us know toilet facilities in schools have been a cause for concern for many pupils.
"The data collected on toilets was an eye opener to many as it told us how young people felt and why they felt it."
Other results from the survey include a quarter of girls and half the boys said they had experienced a lack of privacy.
Nearly half the 224 students spoken to said they avoided using the toilet at school and waited until they got home.
The youth parliament will make seven recommendations to try to make a difference to the life of school students in Medway.
A Medway Council spokesman said: "Good quality and accessible toilets are a key factor from both a health perspective and in promoting a positive learning environment."