Girls have been banned from wearing skirts to school in a bid to protect their modesty.
Glass-sided stairwells have been built in a new building at Stowmarket High School, in Suffolk, and the school's head said he was concerned about personal privacy.
The rule only applies to year seven pupils, joining the school this year, and means children in years eight upwards can still wear skirts until September 2020.
The youngsters have been told they will have to wear trousers, a blazer and clip-on tie.
This uniform replaces the old uniform of skirts, black pullovers or cardigan previously worn by pupils.
The school's website explains that the new policy has been partially put in place because of the new building design.
But the new rules have infuriated parents.
One parent who wanted to remain anonymous told the East Anglian Daily Times : "If this really just about glass side stairs then how come female staff are still wearing skirts? No-one believes this nonsense.
"It's obvious that what is really about is cracking down on girls behaving differently than boys by forcing a gender neutral dress code on them.
"They've exempted teachers because they have a union, while the kids are powerless and so their views count for nothing. It's a disgrace."
However, the school's headteacher, Dave Lee-Allan said: "I was concerned about the new build but have been reassured by the designers that personal privacy has not been an issue in similar buildings.
"The resultant uniform is extremely smart and cheaper than the previous version. It is also designed to be practical - for example we have now have the availability during the summer for students to wear shorts."