Angry parents are in revolt against a headmaster who has introduced a strict new policy on uniforms and untidy hair at his school.
They claim hundreds of pupils at Breda Academy were issued with warning letters in recent days.
Students have been told to change their footwear and hairstyles, while others have been instructed to ensure their tie is properly knotted.
The clampdown by principal Matthew Munro has angered parents at the south Belfast school.
Some 250 parents joined a Facebook page in the space of 24 hours to protest at the strict policy.
Claire Carlin, whose son Jonathan was given a letter, said: "The kids are being picked on constantly because of their hair and shoes."
She said pupils had their jumpers lifted to check their ties were correctly knotted.
However, Mr Munro said parents were advised as far back as June about acceptable uniforms and appearances.
"We just have to get people used to the fact that we have certain expectations - we are not being unreasonable," he said.
Breda Academy, which has 925 pupils, is an amalgamation between Knockbreda High and Newtownbreda High.
Mr Munro previously taught in England. He was headteacher of Meopham School, a mixed non-selective school in Kent.
However, his approach to uniform and appearance has caused controversy.
Advice issued to parents states students "are expected to dress smartly and in compliance with the school uniform requirements".
It adds: "Smart uniform is one way in which we express our readiness for work and our determination to promote a positive image for ourselves and our fellow students within and beyond the school."
The instructions include:
• A school tie of suitable length and size of knot, worn with the top shirt button done up;
• For girls a regulation grey kick pleat skirt worn to the knee;
• Plain black leather formal school shoes. Heavy or reinforced boots, coloured laces and trainers are banned;
• The minimum hair length is a "number two" razor cut with no sharp variations in length for fashion effects.
Ms Carlin said 637 letters were issued earlier this week to pupils who had contravened the regulations.
However, Mr Munro said it was fewer than this, although he was unable to state exactly how many had been issued.
Ms Carlin said her son had been told his hair was too long and too short. She said: "Because he has a number one at the back and sides, and the hair is a wee bit long on top, he was told his hair was too short at the sides and too long at the top.
"He got a letter about it yesterday again."
Ms Carlin said two of her nieces also received letters.
"There's a wee boy who lives down the street from me. He was sent home on Wednesday and told he couldn't come back until his hair grew back," she said.
"What does it matter if your hair is a wee bit long or short?
"It is the same with ties. They are lined up and have their jumpers pulled up to check their ties are done properly. There is a lot of anger among the parents."
Another parent, Sarah McIntyre, said her son, Stan, was told his hair was too short, but claimed others with similar haircuts were ignored.
"It states on the letter that it should be a number two cut. He got a number one - but he wasn't the only one," she said. "He had the same haircut last year and nothing was said about it."
Another said: "There was no issue in previous years. This headmaster has come over and basically turned the school into an army camp."
Other parents took to the 'Breda Academy Parents Views' Facebook page to outline their concerns. One said: "My son has worn the same style of shoes for three years now with no problems. Now we are being told that he needs a new pair for Monday. This school is being pretentious."
A second wrote: "My daughter is in fourth year and has worn the same style shoes every year and now they are sending home letters about them. Unbelievable."
Parents also expressed concerns about long queues at lunchtime, with some claiming their children were unable to get dinner.
Another said her niece was put on the wrong bus and ended up stranded after being dropped off at the wrong place.
Mr Munro conceded there had been some minor problems which would be quickly resolved.
"This is the first week of the operation and we are still getting things in place," he said.
He urged parents with concerns to consider joining the school's Parents, Teachers and Friends Association or become a parent representative on the board of governors.
"This is a new school - this is not Newtownbreda High School or Knockbreda High School," he said. It is a great new opportunity and I'm very pleased with how we've started. People will have concerns, and most of those concerns are being addressed.
"I am speaking to parents and to students. The criticism I take note of, and I will look carefully at what people are saying.
"In terms of uniform, the requirements were shared in June with all parents and put on the website. Where people have purchased in error, they have a period of time to get this fixed."
Asked about pupils having jumpers lifted for tie checks, Mr Munro said: "Some staff check uniform but in an entirely appropriate way. This is not in any way intrusive."