One parent of a secondary school girl told the Daily Express: "She won't use the toilets and tries to last all day. Boys are always speculating on whether girls are having their periods according to how long they take in the toilet."
The mother claims when she spoke to the headmaster she was told her daughter should go to the nurse's office if she has any issues.
The group has found pupils, parents and staff are often too embarrassed to complain about the unisex toilets.
Spokeswoman Helen Raynor said: "No pupil should feel they are unable to use the toilet. No child should avoid school, or stop drinking water so they don't wee."
A Welsh government spokesman said that it will review the findings to see "whether further guidance" is required. It added that when schools are built "stakeholders" are consulted "to ensure the school offers facilities that are fit for purpose".
Hundreds of schools around the UK have adopted unisex toilets.
UNISEX TOILETS IN NZ SCHOOLS
Back home, one of Auckland's top boys' schools has built a new unisex toilet block to cater for transgender students in the future.
It's the latest step Auckland Grammar is taking towards gaining the Rainbow Tick - which specifically recognises and welcomes sexual and gender diversity.
Speaking to Larry Williams on Newstalk ZB in 2018, headmaster Tim O'Connor said the concept came about when school officials realised young men want more privacy in school and public toilets.
"We responded to that, but also in the back of our mind has been diversity, and the reality, that at some point in the future we will have students who identify themselves as transgender or in the LGBT community."
In 2018 O'Connor told the Herald that Auckland Grammar did not have any transgender students attending school at the moment, but they had been thinking about what would happen in the future when it came to accepting students who would not be biologically boys but rather girls transitioning.
"We've thought about it, and for boys' schools it's a big topic being discussed around the world.
"In other countries they're much more advanced in being prepared than we are. In attending those conferences, we've realised we've been a little bit naive, and that we needed to prepare so it's not a shock."
When asked about the reaction from students, O'Connor said he thought adults typically underestimated where the younger generation was at.
"We're the ones who have bigger hang-ups about bigotry and LGBTQ."
He was also confident that homophobia at the school was declining.
"Absolutely. The key is to name it and have conversations with the boys. The use of 'gay' as a colloquial phrase is present in our society, particularly among young people.
"When you name it and say you could actually be offending someone else - our boys have understood that, and we're seeing a positive reaction to it."
