Pupils protesting against a new "gender neutral" uniform were barred from entering their school and sent home on the first day of term.
Dozens of pupils and parents gathered outside Priory School in Lewes, East Sussex, to demonstrate against a rule which bans girls from wearing skirts.
The school said the policy is designed to promote equality.
“Female students locked out of the priory school in Sussex and had the police called on them for refusing to wear 'gender neutral' trousers. Well done girls.
” pic.twitter.com/ZYV8pTUhiT
—
Lisa #PBFB
(@Lisaismyname89) September 6, 2019
Protesting pupils held signs saying "a new uniform for nine months is not sustainable", and "fast fashion is the second biggest contributor to climate change".
Many parents of pupils who attended the demonstration have since received texts from the school asking them to explain their child's "unauthorised absence".
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Local MP Maria Caulfield said she was "very disturbed" to see pupils being turned away.
Tim Loughton MP, who attended Priory School as a child, said it was "political correctness gone mad again".
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Cressida Murray, who helped organise the protest alongside her daughter Libby, said the school's reaction was "outrageous".
She said: "They just weren't prepared and they haven't let anyone in.
"I was hoping there was so many people that they would see sense and let them in."
She said many families cannot afford to buy the uniform, some of whom will need it for less than a year.
Ms Caulfield, MP for Lewes, said on Twitter: "Very disturbed to see the school turning away girls from Priory School because they choose to wear a skirt and calling the police on them.
"This is not how we should be treating the young women of Lewes."
