Kelly Marsh, from Buckshaw Village, says her 16-year-old daughter Bethany fell foul of school rules after completing one of her GCSE exams.
After finishing an exam at St Mary's Catholic School in Leyland, she founded the nearest toilets were locked and says teachers declined to unlock the facility.
The school says the policy was introduced some time ago to encourage pupils to stay in classrooms during lesson times.
However, Kelly says the decision is unfair and potentially placed additional stress on students sitting theirs exams as they are not subject to the same timetable as the rest of the school.
She said: "My daughter is currently sitting her exams and needed the toilet. She waited an hour and a half until the exam had finished to then be told by a teacher that she would have to wait an additional 10 minutes until they were open at lunch.
"The school has taken away their rights to use these toilets during the day, they have locked them and only open them at break and lunch."
She added: "This is disgusting and demeaning that children are being given less human rights than that of somebody in prison.
"This is terrible treatment of pupils and as an adult it can be difficult to “hold it” and what they are doing is wrong.
"I have had two children attend St Mary's and this has never happened before.
She further claims it is placing additional stress on pupils who are already feeling the pressure studying for their exams.
"There are kids with conditions. It's not right. It’s insane and something needs to be done about it.”
Phil Thompson, headteacher at St Mary’s Catholic High School, said: "St Mary’s has a number of toilet blocks which are open throughout the day for pupils to use.
"We encourage pupils to be in class during lesson times, rather than using the toilet. However, pupils with a toilet pass, or in desperate need can go as required."
He added: "There are two blocks which are locked periodically throughout the day, but these can be unlocked on request should the need arise."