A school has been accused of denying its pupils "basic human rights" after lockable gates were put on the toilets to stop them from using the loo during lessons.
Parents are outraged saying their children are now limiting how much they drink and come home with headaches after Hundred of Hoo Academy in Kent imposed the draconian measures.
The rules are said to have left girls unable to change their sanitary protection.
The school, which is rated "good" by Ofsted, said students had long needed a pass to use the toilet during lesson times but had recently introduced "shutters" which have been compared to prison gates.
Staff claim the shutters keep children safe and stop the loos from being vandalised.
Lauren Jewiss, 32, blasted the rules as “ridiculous” and explained pupils have to go to Student Services to request a key for the toilet and then take the key back.
She said: "It's a secondary school and it's a big school - sometimes they have to go from one side to the other to get the key.
"If someone's got a bad tummy or something, it's going to be difficult for them - it's not fair. One of the girls was on her time of the month and they wouldn't let her go. Her mum said just get up and walk out - which she did and then she got in trouble.
"It's basic human rights to go to the toilet. Some students aren't going to the toilet in the day and they have half an hour bus journey home before they can go.
"They haven't been able to go at lunch because there are queues at lunch - so they have to split their lunchtime between eating and queuing for the toilet."
She said on a parents' Facebook page many have called for a petition.
She added: "People are saying it's like a prison. One mum said her daughter almost had an accident."
A furious parent said on Facebook: "My daughter already didn't drink enough at school because of not having enough time to queue for the toilet at break times, so now she drinks even less.
Constantly coming home with a headache."
Another added "this is the same as my daughter", while a third parent claimed her daughter refuses to drink at all.
Another said their daughter refused to drink in the morning before school for the same reason.
The school said it is ‘’renowned for our safeguarding systems" and support.
The school said in a statement: “As part of this safeguarding approach we have always closely monitored pupils' attendance and punctuality to lessons.
"Pupils are able to access toilets, student services and our pastoral rooms throughout the day, but should follow the school systems that have been in place for a number of years, with pupils reminded of them termly.
"There has been no change to policy and pupils are able to use the Academy facilities.
“We have multiple bathrooms around the Academy and pupils use these freely during break and lunch, as staff are on duty in these areas.
"During lesson time pupils should register at their lesson and use the teachers ‘out of lesson’ pass to gain access to the bathrooms or attend one of the pastoral rooms.
“This ensures we know the location of all pupils and can safeguard them effectively.
“Like all schools, we try to encourage students to use the toilets at the most appropriate times to avoid lessons being disruptive, however, if a child needs to use the toilet then they are permitted to do so especially when they have a medical condition that may require it more frequently.
"Shutters are used on-site to prevent unauthorised use of the toilets when they are not supervised which improves both student safety and helps avoid any vandalism.
“We have specifically opted to use shutters rather than doors as this allows a clear view into the communal area of the toilet for staff when walking the site.
"We take our responsibility to safeguard and educate pupils extremely seriously and will continue to support our pupils to be the best that they can be."
