A five-year-old girl was left "distressed" after being forced to share unisex school toilets with boys.
The youngster, called 'C', would often go home in pain after refusing to use the toilets at her primary school in Scotland - and even reduced her liquid intake to limit the need to do so.
Deeming the boys "too noisy", Child C would wait until she got home. The judge later ruled she was a victim of "indirect discrimination".
While both sexes can access the toilet area, each cubicle is marked with 'female' and 'male' signage.
The girl's parents complained about the lack of single-sex facilities, escalating the matter with West Lothian Council.
Now, this week, the judge decided the toilet layout led to indirect discrimination and disadvantaged girls under the Equality Act 2010.
However, the case did not meet the legal threshold for harassment.
Judge Lady Poole ruled: "The particular disadvantage is a combination of the additional issues for girls relating to contamination of hands due to their anatomy and physiology, and the general vulnerability of girls having to perform intimate activities in communal areas.
The situation was described as 'distressing' for the girl
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"These give rise to legitimate considerations of privacy, dignity and health and safety.
"The particular disadvantage arising from provision of all toilets as unisex, relating to contamination of hands and the general vulnerability of girls having to perform intimate activities in communal areas, applies to C."
The judge concluded that the toilet set-up breached section 19 of the Equality Act, adding there was "unlawful indirect discrimination".
The court said the toilets within the school premises went against the requirements of the School Premises (General Requirements and Standards) (Scotland) Regulations 1967.
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The girl's parent's raised the matter with West Lothian Council
|The breach means the school failed to supply separate spaces for both genders which offered up appliances and wash basins to comply with the basic standards for sanitary accommodation.
Under the same regulations, in boys' sanitary accommodation, two thirds of appliances should be urinals - which is also breached by the school's toilet layouts.
Gender critic and author JK Rowling reacted to the news, commenting: "Polite notice to schools still breaking the law by not providing single sex bathrooms: you will be sued and you will lose."
Last year, women's rights campaigners and gender critics were victorious in the Supreme Court landmark ruling that gender refers to biological sex, rather than "gender identity".
Ever since the ruling last April, institutions across the country have been waiting for Labour to hand over trans guidance to implement in toilets, changing rooms and other single-sex spaces.
New guidance was introduced in Parliament around a fortnight ago. Equalities minister Bridget Phillipson has claimed it was designed to protect "people's rights across the country".
She maintained trans people affected by the ruling are "still protected" by the Equality Act.
A West Lothian Council spokesman said: "West Lothian Council has received the court's opinion and will now consider its options.
"In the meantime, the council remains committed to ensuring the highest standard of care for the children and young people attending its schools."