Millie Jones, 11, was not allowed into the building on her first day of secondary school on Wednesday until she changed from a skirt into trousers, her mother has said.

Alice Jones dropped off Millie for her first day at a Co-op Academies Trust school in Failsworth, Oldham. The school has introduced a new policy which requires all students to wear plain black tailored trousers.

The 38-year-old said she knew about the policy but let Millie wear a skirt after she became upset at the thought of wearing trousers. She said a staff member asked her to take Millie home to change, which she refused to do.

Alice said staff later called at about 8.45am to say: "just letting you know that Millie's made her own choice to wear trousers today and enter the building and get on with her day". Alice said Millie had only changed because she was told she could not go in wearing a skirt, and said the row "ruined Millie's milestone moment" starting secondary school.

Several pupils arrived at Co-op Academy wearing skirts, despite the new uniform policy coming into force. The same rule applies at Co-op Academy Walkden, Co-op Academy Swinton, Co-op Academy North Manchester, Co-op Academy Manchester and Co-op Academy Belle Vue.

The mum-of-three, from Oldham, said she has complained to the trust and believes the rule discriminates against girls. She said: "If a girl wants to wear trousers, fine, they should be allowed to wear trousers, but you shouldn't be discriminating against girls and making everyone wear trousers."

Other parents also objected. Samantha Scholes, who has two daughters in Years 10 and 11, said her eldest was turned away on her first day back when she arrived wearing a skirt. Samantha Gallier said her daughter had reluctantly agreed to wear trousers but was upset and said she looked like a boy.

Government guidance says headteachers can discipline pupils who do not wear the correct uniform, but parents can complain if they believe a policy is discriminatory. The Trust says only a small number of pupils have turned up in skirts, were offered a range of trousers to choose from and "have not been turned away".