An academy in Bradford has sent home 152 pupils for arriving at the school gates without meeting its dress code.
Hanson Academy strictly enforced its school uniform policy on Tuesday, with almost 10% of pupils failing to reach the academy's standards.
Angry parents took to the school's Facebook page to complain about the new measures.
But Hanson Academy claims it "communicated clearly" its expectations for this school year.
Pupils face being sent home for a variety of reasons, including if they wear hoop earrings, two earrings or more per ear or patterned trousers.
Students are also not allowed to have an unnatural hair colour or wear jumpers, jackets or coats indoors, and there are strict rules about the type of footwear allowed.
'Ready to learn'
Principal Elizabeth Churton told the BBC that a further 63 pupils were sent home on Wednesday.
She said in an earlier statement: "We explained that students who arrived to school with a uniform issue that could be resolved would be sent home to rectify and parents would be contacted.
"As forewarned, some students were sent home for this reason.
"They were sent home to change and the majority rectified this immediately and returned to school ready to learn."
The principal said rules were an important part of growing up to get students ready for "adult life".
She said: "This is part and parcel of a much wider push on conduct, on behaviour, on attitudes and respect.
"Uniform and the way in which we wear our clothes is all part and parcel of the way in which we communicate with each other.
"It is all part of the educational experience which you would find in any good to outstanding school."
Caren Oxlaide's son was one of those sent home for not wearing the regulation black leather shoes.
She said: "It states black shoes, lace-up, no trainers and flat-soled. That's exactly what his are, pure leather."
She said buying new shoes was not an easy option.
"I can't really afford them, not on income support. But I've got to somehow do it because my son's education is important."
Diane Hickey's daughter Cassidy, 13, was sent home on Wednesday because she was wearing black pumps.
"I'm not buying her a new pair of shoes. I'm a single parent. I can't afford a new pair of shoes," she said.
Another parent expressed concerns about how they were being informed their children had been sent home.
Fiona Taylor, who has two children aged 13 and 11 at the school, said: "Parents yesterday didn't receive text messages until after 14:00.
"So all day their children have been sent away and these parents who were out at work did not get informed until late in the afternoon."
The school insists it will persist with the policy, but Mrs Churton admitted there had been mixed feedback from parents.
She said the school would work with parents who were struggling to dress their children appropriately.